scert.goa.gov.in€¦ · Food : 1 Where Does It Come From? W hat did you eat at home today? Find out what your friend ate today. Did you eat the same kind of food yesterday and today?

Food :Where Does It Come From?1

What did you eat at hometoday? Find out what yourfriend ate today. Did you

eat the same kind of food yesterdayand today? We all eat different kindsof food at different times, isn’t it?

1.1 FOOD VARIETY

Activity 1Ask your friends in the school aboutthe items they would be eating duringa day. See if you can also get thisinformation from friends staying indifferent states of India. List all theitems in your notebook as given inTable 1.1, for as many friends aspossible.

Table 1.1 What do we eat?

ehtfoemaNdneirf/tneduts

smetidooFyadaninetae

There seems to be so muchvariety in the food that we eat. Whatare these food items made of ?

Think about ricecooked at home. Wetake raw rice and boilit in water. Just twomaterials or ing-redients are neededto prepare a dish of boiled rice.

On the other hand, some fooditems are made with manyingredients. To prepare vegetablecurry, we need different kinds ofvegetables, salt, spices, oil and so on.

Activity 2Choose some of the items you listedin Table 1.1 and try to find out whatingredients are used to preparethese, by discussing with yourfriends and elders at home. List themin Table 1.2. Some examples aregiven here. Add some more items tothis list.

Table 1.2 Food items and theiringredients

metIdooF stneidergnI

itoR / itapahc attA retaw,

laD/lio,tlas,retaw,sesluP

eehg secips,

SCIENCE2

What do we find? Do we find some ingredientscommon for different food items? Discuss in class.

So, where do these ingredients come from?

1.2 FOOD MATERIALS AND SOURCES

It may be easy for us to guess the sources of some ofthe ingredients that we listed in Table 1.2. Fruits andvegetables, for instance. Where do they come from?Plants, of course! What are the sources of rice orwheat? You may have seen paddy or wheat fields withrows and rows of plants, which give us these grains.

And then, there are food items like milk, eggs, meat,chicken, fish, prawns, beef, pork and such others,which come from animals.

Activity 3

Let us take the food items listedearlier and try to find out where theycome from — the ingredients andtheir sources. Some examples areshown in Table 1.3. complete theTable 1.3 and add more examples tothis list.

metIdooF stneidergnI secruoS

ildI eciR tnalP

laddarU

tlaS

retaW

nekcihCyrruc nekcihC laminA

secipS

/liO eehg /stnalPslaminA

retaW

reehK kliM laminA

eciR tnalP

raguS

Table 1.3 Ingredients used toprepare food items and

their sources

3FOOD: WHERE DOES IT COME FROM?

What do we conclude from Activity3? Plants are the sources of foodingredients like grains, cereals,vegetables and fruits. Animalsprovide us with milk, meat and eggs.Cows, goats and buffaloes are somecommon animals which give us milk.Milk and milk products like butter,cream, cheese and curd are used allover the world. Can you name someother animals which give us milk?

1.3 PLANT PARTS AND ANIMAL

PRODUCTS AS FOOD

Plants are one source of our food.Which parts of a plant are these?

We eat many leafy vegetables. Weeat fruits of some plants. Sometimesroots, sometimes stems and evenflowers. Have you ever eaten pumpkinflowers dipped in

Table 1.4 Plant parts as food

tnalphtiwmetidooFecruosrojamehtsa

ecruos/stneidergnI sevighcihwtraptnalPtneidergniehtsu

yrruclajnirB.1 lajnirB tiurF

)rehtoyna(ecipssaillihC tiurF

,dratsum,tundnuorgmorfliOtnalprehtoyna,naebyos deeS

.2

.3

Paheli wants to know if any ofour food comes from sourcesother than plantsand animals.

Flower

Bud

Roots

Stem

Leaf

rice paste andfried? Try it!

Some plantshave two or moreedible (eatable)parts. Seeds ofmustard plantsgive us oil and theleaves are used asa vegetable. Canyou think of thedifferent parts ofa banana plantthat are used as food? Think of moreexamples where many parts of asingle plant are used as food.

Activity 4

From all the food items you havelisted in Table 1.3, choose thoseitems whose ingredients areobtained from plants. Which part ofa plant? Identify these and list thefood items and plant parts as shownin Table 1.4.

Activity 5

SCIENCE4

Take some dry seeds of moong orchana. Put a small quantity of seedsin a container filled with water andleave this aside for a day. Next day,drain the water completely and leavethe seeds in the vessel. Wrap themwith a piece of wet cloth and setaside. The following day, do youobserve any changes in the seed? A

small white structure may havegrown out of the seeds. If so, theseeds have sprouted. If not, wash theseeds in water, drain the water andleave them aside for another day,covered with a wet cloth. The nextday, see if the seeds have sprouted.

After washing these sproutedseeds, you can eat them. They canalso be boiled. Add some spices andget a tasty snack to eat.

Do you know where honey comesfrom, or how it is produced? Have

you seen abeehive where somany bees keepbuzzing about?Bees collectnectar (sweetjuices) fromflowers, convert itinto honey andstore it in theirhive. Flowers andtheir nectar may be available only fora part of the year. So, bees store thisnectar for their use all through theyear. When we find such a beehive,we collect the food stored by the beesas honey.

1.5 WHAT DO ANIMALS EAT?Do you have cattle or a pet that youtake care of? A dog, cat, buffalo or agoat? You will then surely be awareof the food, the animal eats. Whatabout other animals? Have you everobserved what a squirrel, pigeon,lizard or a small insect may be eatingas their food?

Activity 6

Several animals are listed in Table1.5. For some of them, the type of

Do not try to test unknown plantsaround you to see if they are edible!Some plants could be poisonous.


food they eat is also given. Fill in theblanks in the table.

Activity 7

Have a look again at Table 1.5 andgroup the animals entered here asfollows. Place animals which eat only

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ehtdooFstaelamina

olaffuB ,ekaclio,ssarGsniarg,yah

taC ,slaminallamSklim,sdrib

taR

noiL

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redipS

drazilesuoH

woC

sgniebnamuH

ylfrettuB

worC

srehtO

plants or plant products in Group1. These are called herbivores. Thereare some animals which eat otheranimals. Place these in Group 2.These animals are called carnivores.Do you find some animals which eatboth plants and animals? Place themin Group 3. These are calledomnivores. Prepare a table as inTable 1.6 and enter these separatelyin the three columns, as shown.

We know that there are manyamongst us, who do not get sufficientfood. We need to find ways by whichmore food can be grown in thecountry. That will not be enough; wewill need to find ways to ensure thatthis food is made easily available toeach and every one of us.

Paheli wants to know whereyou would place humanbeings, while fillingTable 1.6.

Table 1.6

serovibreH serovinraC serovinmO

woC noiL goDTable 1.5 Animals and their food

Group 1 Group 2 Group 3

SCIENCE6

stneidergnI

elbidE

ratceN

sdeesdetuorpS

erovibreH

erovinraC

erovinmO

There is a lot of variation in the food eaten in different regions of India.

The main sources of our food are plants and animals.

Animals which eat only plants are called herbivores.

Animals which eat only animals are called carnivores.

Animals which eat both plants as well as other animals are calledomnivores.

1. Do you find that all living beings need the same kind of food?

2. Name five plants and their parts that we eat.

3. Match the items given in Column A with that in Column B

AnmuloC BnmuloC

,druc,kliM reenap , eehg , slaminarehtotae

torrac,rewolfiluac,hcanipS stcudorptnalpdnastnalptae

sregitdnasnoiL selbategevera

serovibreH stcudorplaminallaera

Summary

Exercises

Key Words


SUGGESTED PROJECTS AND ACTIVITIES

1. You must have seen a garden lizard around your home. Next time whenever you see it,observe carefully and find out what it takes for food. Is the food different from that of ahouse lizard?

2. Make a list (with pictures, when possible) of food items generally taken by people ofdifferent regions of India. Place these on a large outline map of India to display in yourclassroom.

3. Find out the names of plants that grow in water and which are eatenas food.

4. In Chapter 10, you will find out ways of measuring length of curved lines. In your math-ematics classes you will learn to prepare bar graphs. After you learn these, try the follow-ing interesting project. Prepare some sprouts of moong as discussed in the chapter. Washthem in water everyday and drain all the water. Let them grow for a week until the wholeof the seeds grow into young plants. Measure the lengths of the sprouts everyday using astring. Take care that they do not break. Prepare a bar graph of the number of sproutshaving lengths in different ranges.

THINGS TO THINK ABOUT

1. Does everyone around you get enough food to eat? If not, why ?

2. What are the ways we can think of to avoid wastage of food ?

4. Fill up the blanks with the words given:

herbivore, plant, milk, sugarcane, carnivore

(a) Tiger is a ____________________ because it eats only meat.

(b) Deer eats only plant products and so, is called ______________.

(c) Parrot eats only _________________ products.

(d) The ________________ that we drink, which comes from cows, buffaloes andgoats is an animal product.

(e) We get sugar from ___________________.

Components of Food2In Chapter 1, we made lists of the

food items that we eat. We alsoidentified food items eaten in

different parts of India and markedthese on its map.

A meal could consist of chapati,dal and brinjal curry. Another maybe rice, sambar and a vegetablepreparation of lady’s finger (bhindi).Yet another meal could be appam,fish curry and vegetables.

Activity 1

Our meals usually have at least oneitem made of some kind of grain.Other items could be a dal or a dishof meat and vegetables. It may alsoinclude items like curd, butter milk

and pickles. Some examples of mealsfrom different regions are given inTable 2.1. Select food items youdepicted on the map in Chapter 1.Add some more meals to this list andenter these in Table 2.1.

Sometimes, we may not reallyhave all this variety in our meals. Ifwe are travelling, we may eatwhatever is available on the way. Itmay not be possible for some of us,to eat such a variety of items, mostof the time.

There must be some reasonthough, why meals usually consistof such a distribution. Do you thinkthat our body needs different kindsof food for some special purpose?

2.1 WHAT DO DIFFERENT FOOD

ITEMS CONTAIN?We know that each dish is usuallymade up of one or more ingredients,which we get from plants or animals.

Table 2.1 Some common meals of different regions/states

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d la taem/selbategeV rehtO s

bajnuP ikkaM )nroc( itor amjaR)snaebyendiK(

gaasnosraS)yrrucfaeldratsuM(

,druC eehg

arhdnAhsedarP eciR ladrauT dna

masar ( urahc ) urudnuK ( iakadnod ) ,klimrettuB eehg ,(elkcip iakavaa )

9COMPONENTS OF FOOD

These ingredients contain somecomponents that are needed by ourbody. These components are callednutrients. The major nutrients inour food are namely carbohydrates,proteins, fats, vitamins and minerals.In addition, food contains dietaryfibres and water which are alsoneeded by our body.

Do all foods contain all thesenutrients? With some simplemethods we can test whether cookedfood or a raw ingredient contains oneor more of these nutrients. The testsfor presence of carbohydrates,proteins and fats are simpler to doas compared to the tests for othernutrients. Let us do these tests andrecord all our observationsin Table 2.2.

For carrying out these tests, youwill need solutions of iodine, coppersulphate and caustic soda. You willalso need a few test tubes and adropper.

Try these tests on cooked fooditems as well as raw materials. Table2.2 shows you a way to record theobservations from these tests. Somefood items are given in this table. Youcan conduct the tests either withthese or any other available fooditems. Do these tests carefully and donot try to eat or taste any chemicals.

If the required solutions are notavailable in readymade form, yourteacher can prepare them as follows.

Let us begin by testing differentfood items to see if they containcarbohydrates. There are many

types of carbohydrates. The maincarbohydrates found in our food arein the form of starch and sugars. Wecan easily test if a food item containsstarch.

Activity 2

Test for StarchTake a small quantity of a food itemor a raw ingredient. Put 2-3 drops ofdilute iodine solution on it (Fig. 2.1).

ebnacenidoifonoitulosetulidA

fospordwefagniddaybderaperp

dellifflahebuttsetaotenidoierutcnit

.retawhtiw

ebnacnoitulosetahplusreppoC

fo)g(marg2gnivlossidybderaperp

)Lm(ertilillim001nietahplusreppoc

.retawfo

nidevlossidadoscitsuacfog01

deriuqerehtsekamretawfoLm001

.adoscitsuacfonoitulos

Fig. 2.1 Testing for starch

10 SCIENCE

Observe if there is any change in thecolour of the food item. Did it turnblue-black? A blue-black colourindicates that it contains starch.

Repeat this test with other fooditems to find out which of thesecontain starch. Enter all yourobservations in Table 2.2.

Test for ProteinTake a small quantity of afood item for testing. If thefood you want to test is asolid, you first need tomake a paste of it orpowder it. Grind or masha small quantity of the fooditem. Put some of this in aclean test tube, add 10drops of water to it andshake the test tube.

Now, using a dropper,add two drops of solutionof copper sulphate and ten

drops of solution of caustic soda tothe test tube (Fig. 2.2). Shake welland let the test tube stand for a fewminutes. What do you see? Did thecontents of the test tube turn violet?A violet colour indicates presence ofproteins in the food item.

Now, you can repeat this test onother food items.

metidooF hcratS)tneserp(

nietorP)tneserp(

taF)tneserp(

otatopwaR seY

kliM seY

tundnuorG seY

dekoocnUderedwop

ecir

ecirdekooC

tunococyrD

dekoocnUraut lad

)deredwop(

dekooC lad

ynafoecilsAelbategev

ynafoecilsAtiurf

ggedelioBetihw(

)noitrop

Fig. 2.2 Testing for protein

Table 2.2 Nutrients present in some food items

11COMPONENTS OF FOOD

(a)Groundnuts

Nuts

Til

Test for FatsTake a small quantity of a food item.Wrap it in a piece of paper and crushit. Take care that the paper does nottear. Now, straighten the paper andobserve it carefully. Does it have anoily patch? Hold the paper againstlight. Are you able to see the lightfaintly, through this patch?

An oily patch on paper shows thatthe food item contains fat. The fooditems may sometimes contain a littlewater. Therefore, after you haverubbed an item on paper, let thepaper dry for a while. If there wereany water that may have come fromfood, it would dry up after some time.If no oily patch shows up after this,the food item does not contain anyfat.

What do these tests show? Arefats, proteins and starch present inall the food items that you tested?Does a food item contain more thanone nutrient? Do you find any fooditem that does not contain any ofthese nutrients?

We tested food items for threenutrients — carbohydrates, proteinsand fats. There are also othernutrients like vitamins andminerals that are present in differentfood items. Why do we need all thesenutrients?

2.2 WHAT DO VARIOUS NUTRIENTS

DO FOR OUR BODY?Carbohydrates mainly provide

energy to our body. Fats also giveus energy. In fact, fats give muchmore energy as compared to thesame amount of carbohydrates.Foods containing fats and carbo-hydrates are also called ‘energygiving foods’ (Fig. 2.3 and Fig. 2.4).

Fig. 2.4 Some sources of fats: (a) plantsources and (b) animal sources

(b)

Meat

Fig. 2.3 Some sources of carbohydrates

SugarcaneSweet potato

Wheat

Rice

Bajra

Melon

Mango

Potato

Maize

Papaya

12 SCIENCE

Proteins are needed for the growthand repair of our body. Foodscontaining proteins are often called‘body building foods’ (Fig 2.5).

Vitamins help in protecting ourbody against diseases. Vitamins alsohelp in keeping our eyes, bones, teethand gums healthy.

Vitamins are of different kindsknown by different names. Some ofthese are Vitamin A, Vitamin C,Vitamin D, Vitamin E and K. Thereis also a group of vitamins calledVitamin B-complex. Our body needs

all types of vitamins in smallquantities. Vitamin A keeps our skinand eyes healthy. Vitamin C helpsbody to fight against many diseases.Vitamin D helps our body to usecalcium for bones and teeth. Foodsthat are rich in different vitamins areshown in Fig. 2.6 to Fig. 2.9.

Minerals are needed by our bodyin small amounts. Each one isessential for proper growth of body

Fig. 2.5 Some sources of proteins: (a) plantsources and (b) animal sources

Peas

Gram Moong Dal

Beans

Soyabeans(a)

Meat

Eggs

Fish

Paneer (b)

Fig. 2.6 Some sources of Vitamin A

Liver

Guava

Lemon

Amla

Fig. 2.7 Some sources of Vitamin B

Fig. 2.8 Some sources of Vitamin C

Tomato

Orange

Fig. 2.9 Some sources of Vitamin D


and to maintain good health. Somesources of different minerals areshown in Fig. 2.10.

Most food items, usually, havemore than one nutrient. You mayhave noticed this, while recordingyour observations in Table 2.2.However, in a given raw material, oneparticular nutrient may be presentin much larger quantity than inothers. For example, rice has morecarbohydrates than other nutrients.Thus, we say that rice is a“carbohydrate rich” source of food.

Besides these nutrients, our bodyneeds dietary fibres and water.Dietary fibres are also known asroughage. Roughage is mainlyprovided by plant products in ourfoods. Whole grains and pulses,potatoes, fresh fruits and vegetablesare main sources of roughage.Roughage does not provide anynutrient to our body, but is anessential component of our food andadds to its bulk. This helps our bodyto get rid of undigested food.

Our body also prepares VitaminD in the presence of Sunlight

Fig. 2.10 Sources of some minerals

Some sourcesof calcium

Some sourcesof iron

Some sources ofphosphorous

Some sourcesof iodine

14 SCIENCE

Water helps our body to absorbnutrients from food. It also helps inthrowing out some wastes from bodyas urine and sweat. Normally, we getmost of the water that our bodyneeds from the liquids we drink —such as water, milk and tea. Inaddition, we add water to mostcooked foods. Let’s see if there is anyother source which provides water toour body.

Activity 3

Take a tomato or a fruit like lemon.Cut it into small pieces. Do yourhands get wet while doing so?

Carefully observe whenevervegetables and fruits are being cut,peeled, grated or mashed at yourhome. Do you find any freshvegetables or fruits that do notcontain some amount of water?

We see that many food materialsthemselves contain water. To someextent, our body needs are met bythis water. Apart from this, we alsoadd water while cooking many fooditems.2.3 BALANCED DIET

The food we normally eat in a day isour diet. For growth andmaintenance of good health, our dietshould have all the nutrients that ourbody needs, in right quantities. Nottoo much of one and not too little ofthe other. The diet should alsocontain a good amount of roughageand water. Such a diet is called abalanced diet.

Do you think that people of all agesneed the same type of diet? Do youalso think that, what we need for abalanced diet would depend on theamount of physical work that we do?

Prepare a chart of whatever youeat over a period of a week. Checkwhether all the nutrients mentionedare present in one or the other fooditems being eaten within a day or so.

Pulses, groundnut, soybean,sprouted seeds (moong and Bengalgram), fermented foods (South Indianfoods such as idlis), a combinationof flours (missi roti, thepla made fromcereals and pulses), banana,spinach, sattu, jaggery, availablevegetables and other such foodsprovide many nutrients. Therefore,one can eat a balanced diet withoutexpensive food materials.

Eating the right kind of food is notenough. It should also be cookedproperly so that its nutrients are not

lost. Are you aware that somenutrients get lost in the process ofcooking and preparations ?

Paheli wonders whether animalfood also consists of these differentcomponents and do they also needa balanced diet?


If the vegetables and fruits arewashed after cutting or peeling them,it may result in the loss of somevitamins. The skins of manyvegetables and fruits containvitamins and minerals. Similarly,repeated washing of rice and pulsesmay remove some vitamins andminerals present in them.

We all know that cookingimproves the taste of food and makesit easier to digest. At the same time,cooking also results in the loss ofcertain nutrients. Many usefulproteins and considerable amountsof minerals are lost if excess water isused during cooking and is thenthrown away.

Vitamin C gets easily destroyed byheat during cooking. Would it not besensible to include some fruits andraw vegetables in our diet?

Boojho thought that fats wouldbe the best foods to eat, all the time.A katori of fat will give much moreenergy than a katori of carbohydraterich food, isn’t it? So, he ate nothing

but food rich in fats — fried food likesamosa and poori, malai, rabdi andpeda.

Do you think he was right? No, ofcourse not! It can be very harmfulfor us to eat too much of fat rich foodsand we may end up suffering from acondition called obesity.

2.4 DEFICIENCY DISEASES

A person may be getting enough foodto eat, but sometimes the food maynot contain a particular nutrient. Ifthis continues over a long period oftime, the person may suffer from itsdeficiency. Deficiency of one or morenutrients can cause diseases ordisorders in our body. Diseases thatoccur due to lack of nutrients over along period are called deficiencydiseases.

If a person does not get enoughproteins in his/her food for a longtime, he/she is likely to have stuntedgrowth, swelling of face, discolou-ration of hair, skin diseases anddiarrhoea.

If the diet is deficient in bothcarbohydrates and proteins for a longperiod of time, the growth may stopcompletely. Such a person becomesvery lean and thin and so weak thathe/she may not even be able to move.

Deficiency of different vitaminsand minerals may also result incertain diseases or disorders. Someof these are mentioned in Table 2.3.

All deficiency diseases can beprevented by taking a balanced diet.

In this chapter, we askedourselves the reason why widely

16 SCIENCE

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setardyhobraC

ygrenE

staF

slareniM

stneirtuN

snietorP

egahguoR

yvrucS

hcratS

snimatiV

Table 2.3 – Some diseases/disorders caused bydeficiency of vitamins and minerals

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ycneicifeD/esaesid redrosid smotpmyS

AnimatiV noisivfossoL

fossol,noisivrooPssenkradninoisivsemitemos,)thgin(

noisivfossoletelpmoc

nimatiV1B irebireB

W dnaselcsumkaeotygreneelttilyrev

krow

CnimatiV yvrucSB ,smuggnideel

regnolekatsdnuowlaehotemit

DnimatiV stekciR B tfosemocebsenotnebdna

muiclaC htootdnaenoByaced

htoot,senobkaeWyaced

enidoI retioG

G kcenehtnisdnal,nellowsraeppa

niytilibasidlatnemnerdlihc

norI aimeanA W ssenkae

varying food from different regions had a commondistribution. This distribution, we find, ensures thatour meals have a balance of the different nutrientsneeded by the body.

The major nutrients in our food are carbohydrates, proteins, fats,vitamins and minerals. In addition, food also contains dietary fibres andwater.

Carbohydrates and fats mainly provide energy to our body.

Proteins and minerals are needed for the growth and the maintenanceof our body.

Vitamins help in protecting our body against diseases.

Balanced diet provides all the nutrients that our body needs, in rightquantities, along with adequate amount of roughage and water.

Deficiency of one or more nutrients in our food for a long time maycause certain diseases or disorders.

Summary

Key Words



1. Prepare a diet chart to provide balance diet to a twelve year old child. Thediet chart should include food items which are not expensive and are com-monly available in your area.

2. We have learnt that excess intake of fats is harmful for the body. Whatabout other nutrients? Would it be harmful for the body to take too muchof proteins or vitamins in the diet? Read about diet related problems to findanswers to these questions and have a class discussion on this topic.

3. Test the food usually eaten by cattle or a pet to find out which nutrients arepresent in animal food. Compare results obtained from the whole class toconclude about balanced diet requirements for different animals.

1. Name the major nutrients in our food.

2. Name the following:

(a) The nutrients which mainly give energy to our body.

(b) The nutrients that are needed for the growth and maintenance of our body.

(c) A vitamin required for maintaining good eyesight.

(d) A mineral that is required for keeping our bones healthy.

3. Name two foods each rich in:

(a) Fats

(b) Starch

(c) Dietary fibre

(d) Protein

4. Tick (√) the statements that are correct.

(a) By eating rice alone, we can fulfill nutritional requirement of our body. ( )

(b) Deficiency diseases can be prevented by eating a balanced diet. ( )

(c) Balanced diet for the body should contain a variety of food items. ( )

(d) Meat alone is sufficient to provide all nutrients to the body. ( )

5. Fill in the blanks.

(a) ______________ is caused by deficiency of Vitamin D.

(b) Deficiency of ______________ causes a disease known as beri-beri.

(c) Deficiency of Vitamin C causes a disease known as ______________.

(d) Night blindness is caused due to deficiency of ____________ in our food.

Exercises

Fibre to Fabric3Paheli and Boojho won the first

prize in a Science Quizcompetition held at their

school. They were very excited anddecided to use the prize money to buyclothes for their parents. When theysaw a large variety of cloth material,they got confused (Fig. 3.1). Theshopkeeper explained that someclothes or fabrics were cotton andsome were synthetic. He also hadwoollen mufflers and shawls. Therewere many silk sarees as well. Paheliand Boojho felt very excited. Theytouched and felt these differentfabrics. Finally, they bought awoollen muffler and a cotton saree.

After their visit to the cloth shop,Paheli and Boojho began to noticevarious fabrics in their surroundings.They found that bed sheets, blankets,

curtains, tablecloths, towels anddusters were made from differentkinds of fabrics. Even their schoolbags and the gunny bags were madefrom some kind of fabric. They triedto identify these fabrics as cotton,wool, silk or synthetic. Can you alsoidentify some fabrics?

3.1 VARIETY IN FABRICS

Activity 1Visit a nearbytailoring shop.Collect cuttings offabrics leftoverafter stitching.Feel and toucheach piece offabric. Now, try tolabel some of thefabrics as cotton, silk, wool orsynthetic after asking for help fromthe tailor.

Do you wonder what thesedifferent fabrics are made of? Whenyou look at any fabric, it seems acontinuous piece. Now, look at itclosely. What do you notice (Fig. 3.2)?

Activity 2

Select a piece of cotton fabric youlabelled in Activity 1. Now, try to finda loose thread or yarn at one of the

Fig. 3.1 A cloth shop

Fig.3.2 Enlargedview of a piece of

fabric

19FIBRE TO FABRIC

edges and pull it out (Fig. 3.3). If noloose yarns are visible, you cangently pull one out with a pin or aneedle.

We find that a fabric is made upof yarns arranged together. What arethese yarns made of?

3.2 FIBRE

Activity 3Take out a yarn from a piece of cottonfabric. Place this piece of yarn on thetable. Now, press one end of the yarnwith your thumb. Scratch the otherend of the yarn along its length withyour nail as shown in Fig. 3.4. Doyou find that at this end, the yarnsplits up into thin strands (Fig. 3.5)?

You might have observedsomething similar when you try tothread a needle. Many a time, theend of the thread is separated intoa few thin strands. This makes itdifficult to pass the thread throughthe eye of the needle. The thinstrands of thread that we see, aremade up of still thinner strandscalled fibres.

Fabrics are made up of yarns andyarns are further made up of fibres.Where do these fibres come from?

The fibres of some fabrics suchas cotton, jute, silk and wool areobtained from plants and animals.These are called natural fibres.Cotton and jute are examples offibres obtained from plants. Wool andsilk fibres are obtained from animals.Wool is obtained from the fleece ofsheep or goat. It is also obtained fromthe hair of rabbits, yak and camels.Silk fibre is drawn from the cocoonof silkworm.

For thousands of years naturalfibres were the only source availablefor making fabrics. In the lasthundred years or so, fibres are alsomade from chemical substances,

Fig. 3.3 Pulling a thread from a fabric

Fig.3.4 Splitting the yarn into thin strands

Fig. 3.5 Yarn split up into thin strands

Boojho has seen in themuseums, items like theone shown here. Thesewere worn by warriors.He wants to know ifthese are made ofsome kinds of fibre.

20 SCIENCE

which are not obtained from plantor animal sources. These are calledsynthetic fibres. Some examples ofsynthetic fibres are polyester, nylonand acrylic.

3.3 SOME PLANT FIBRES

CottonHave you ever made wicks for oillamps? What do you use for makingthese wicks? This cotton wool is alsoused for filling mattresses, quilts orpillows.

Take some cotton wool, pull itapart and look at its edges. What doyou observe? The small, thin strandsthat you see are made up of cottonfibres.

Where does this cotton wool comefrom? It is grown in the fields. Cottonplants are usually grown at placeshaving black soil and warm climate.Can you name some states of ourcountry where cotton is grown? Thefruits of the cotton plant (cottonbolls) are about the size of a lemon.After maturing, the bolls burst open

and the seeds covered with cottonfibres can be seen. Have you everseen a cotton field that is ready forpicking? It looks like a field coveredwith snow (Fig.3.6).

From these bolls, cotton is usuallypicked by hand. Fibres are thenseparated from the seeds by combing.This process is called ginning ofcotton. Ginning was traditionallydone by hand (Fig.3.7). These days,machines are also used for ginning.

JuteJute fibre is obtained from the stemof the jute plant (Fig 3.8). It iscultivated during the rainy season.In India, jute is mainly grown in West Bengal, Bihar andAssam. The juteplant is normallyharvested when itis at floweringstage. The stems ofthe harvestedplants are imme-rsed in water fora few days. Thestems rot andfibres are separ-ated by hand.Fig.3.6 Field of cotton plants

Fig. 3.7 Ginning of cotton

Fig. 3.8 A jute plant

21FIBRE TO FABRIC

To makefabrics, all thesefibres are firstconverted intoyarns. How is itdone?

3.4 SPINNING COTTON YARN

You can try making cotton yarnyourself.

Activity 4Hold some cotton wool inone hand. Pinch somecotton between thethumb and forefinger ofthe other hand. Now,gently start pulling out thecotton, while continuouslytwisting the fibres (Fig.3.9). Are you able to makea yarn?

The process of makingyarn from fibres is calledspinning. In this process,fibres from a mass ofcotton wool are drawn outand twisted. This bringsthe fibres together to forma yarn.

A simple device usedfor spinning is a handspindle, also called takli(Fig. 3.10). Another handoperated device usedfor spinning is charkha

(Fig. 3.11). Use of charkha waspopularised by Mahatma Gandhi aspart of the Independence movement.He encouraged people to wear clothesmade of homespun yarn and shunimported cloth made in the mills ofBritain.

Spinning of yarn on a large scaleis done with the help of spinningmachines. After spinning, yarns areused for making fabrics.

3.5 YARN TO FABRIC

There are many ways by whichfabrics are made from yarns. The twomain processes are weaving andknitting.

WeavingIn Activity 2, you might have noticedthat a fabric is made up of two setsof yarns arranged together. Theprocess of arranging two sets of yarnstogether to make a fabric is calledweaving. Let us try to weave somepaper strips.

Activity 5Take two sheets of paper of differentcolours. Cut square pieces of lengthand width equal to 30 cm from eachsheet. Now, fold both the sheets intohalf. On one sheet draw lines as

Fig. 3.9 Making yarn from cotton

Fig. 3.10A Takli

Fig. 3.11 Charkha

22 SCIENCE

shown in the Fig 3.12 (a) and on theother as shown in Fig.3.12 (b). Cutboth the sheets along the dottedlines and then unfold. Weave thestrips one by one through the cutsin the sheet of paper as shown inFig.3.12 (c). Fig. 3.12 (d) shows thepattern after weaving all the strips.

In a similar manner, two sets ofyarn are woven to make a fabric. Theyarns are much thinner than ourpaper strips, of course! Weaving offabric is done on looms (Fig. 3.13).The looms are either hand operatedor power operated.

KnittingHave you noticed how sweaters areknitted? In knitting, a single yarn

Fig. 3.12 Weaving with paper strips

(a)(c)

(d)

(b)

Fig. 3.13 Handloom

is used to make a piece of fabric (Fig.3.14). Have you ever pulled the yarnfrom a torn pair of socks? Whathappens? A single yarn gets pulledout continuously as the fabric getsunravelled. Socks and many otherclothing items are made of knittedfabrics. Knitting is done by handand also on machines.

Fig 3.14 Knitting

Paheli wants to know if youhave seen any fabrics that aremade of the fibres on the outercovering of coconut. What arethese fibres normallyused for?

23FIBRE TO FABRIC

Weaving and knitting are used formaking different kinds of fabric.These fabrics are used for a varietyof clothing items.

3.6 HISTORY OF CLOTHING MATERIAL

Have you ever wondered whatmaterials people used in ancienttimes for clothes? It appears that inthose times people used the bark andbig leaves of trees or animal skinsand furs to cover themselves.

After people began to settle in agri-cultural communities, they learnt toweave twigs and grass into mats andbaskets. Vines, animal fleece or hairwere twisted together into longstrands. These were woven intofabrics. The early Indians wore fabricsmade out of cotton that grew in the

loownottoC

cirbaF

erbiF

gnittinK

gninnipS

gnivaeW

nraY

There is a variety of clothing material or fabric, such as, cotton, silk,wool and polyester.

regions near the river Ganga. Flax isalso a plant that gives natural fibres.In ancient Egypt, cotton as well asflax were cultivated near the river Nileand were used for making fabrics.

In those days, stitching was notknown. People simply draped thefabrics around different parts of theirbody. Many different ways of drapingfabrics were used. With the inventionof the sewing needle, people startedstitching fabrics to make clothes.Stitched clothes have gone throughmany variations since this invention.But, is it not amazing that even todaysaree, dhoti, lungi or turban is usedas an un-stitched piece of fabric?

Just as there is a large variety inthe food eaten all over our country,a large variety exists also in fabricsand clothing items.

Summary

Key Words

24 SCIENCE

1. Classify the following fibres as natural or synthetic:

nylon, wool, cotton, silk, polyester, jute

2. State whether the following statements are true or false:

a) Yarn is made from fibres.

b) Spinning is a process of making fibres.

c) Jute is the outer covering of coconut.

d) The process of removing seed from cotton is called ginning.

e) Weaving of yarn makes a piece of fabric.

f) Silk fibre is obtained from the stem of a plant.

g) Polyester is a natural fibre.

3. Fill in the blanks:

a) Plant fibres are obtained from_________ and ________ .

b) Animals fibres are __________ and ___________ .

4. From which parts of the plant cotton and jute are obtained?

5. Name two items that are made from coconut fibre.

6. Explain the process of making yarn from fibre.


1. Visit a nearby handloom or powerloom unit and observe the weaving or knit-ting of fabric.

2. Find out if any crop is grown in your region for obtaining fibre. If yes, what isit used for?

3. India has been a major producer of cotton and its fabric. India exports cottonfabrics and items to many other countries. Find out, how it helps us?

Fabrics are made from yarns, which in turn are made from fibres.

Fibres are either natural or synthetic. Cotton, wool, silk and jute aresome natural fibres, while nylon and polyester are some examples ofsynthetic fibres.

Fibres like cotton and jute are obtained from plants.

The process of making yarn from fibres is called spinning.

Fabric from yarns is made by weaving and knitting.

Exercises

25FIBRE TO FABRIC

Boojho knows that burning ofcotton yarn gives an odour similarto burning paper. He is wonderingif he can assume that paper is alsomade from plants.

4. Do you know that famous Sufi Saint and poet Kabir, was a weaver? Find outabout his life and teachings.

5. You can do an activity to identify the yarns of a fabric under the supervisionof your teacher or parents. Pull out six to eight yarns from the fabric. Holdone end of the yarn with a tong and bring the other end over the flame of acandle. Observe carefully. Do the yarns shrink away from the flame? Do theyarns melt or burn? What type of odour is given off? Note down your obser-vations.

If these are cotton yarns, they burn but do not shrink or melt. The burningyarn gives an odour similar to burning paper. The silk yarn shrinks awayfrom the flame and burns but does not melt. It has the odour of charredmeat. The wool yarn also shrinks and burns but does not melt. It has astrong odour of burning hair. The synthetic yarns shrink and burn. Theyalso melt and give out an odour similar to burning plastics.

26 SCIENCE

SortingMaterials into Groups4

4.1 OBJECTS AROUND US

We saw that our food and clothes haveso much variety in them. Not justfood and clothes, there is such a vastvariety of objects everywhere. We seearound us, a chair, a bullock cart, acycle, cooking utensils, books,clothes, toys, water, stones and manyother objects. All these objects havedifferent shapes, colours and uses(Fig. 4.1).

Look around and identify objectsthat are round in shape. Our list mayinclude a rubber ball, a football anda glass marble. If we include objectsthat are nearly round, our list could

Fig. 4.1 Objects around us

also include objects like apples,oranges, and an earthen pitcher(gharha). Suppose we were lookingfor objects that are edible. We mightinclude all the items that we havelisted in Tables 1.1, 1.2 and 1.3 inChapter 1. We might also find thatsome of those round shaped objectswe just listed out, are also in thisgroup.

Let us say, we wish to make agroup of objects that are made ofplastics. Buckets, lunch boxes, toys,water containers, pipes and manysuch objects, may find a place in thisgroup. There are so many ways togroup objects! In the above exampleswe have grouped objects on the basisof their shape or the materials theyare made from.

All objects around us are made ofone or more materials. Thesematerials may be glass, metal,plastics, wood, cotton, paper, mud orsoil. Can you think of more examplesof materials?

Activity 1

Let us collect as many objects aspossible, from around us. Each of uscould get some everyday objects fromhome and we could also collect someobjects from the classroom or fromoutside the school. What will we have

27SORTING MATERIALS INTO GROUPS

in our collection? Chalk, pencil,notebook, rubber, duster, a hammer,nail, soap, spoke of a wheel, bat,matchbox, salt, potato! We can alsolist objects that we can think of, but,cannot bring to the classroom. Forexample, wall, trees, doors, tractor,road.

Separate all objects from thiscollection that are made from paperor wood. This way we have divided allobjects into two groups. One grouphas the objects that are made frompaper or wood while the other grouphas the objects that are not made ofthese materials. Similarly, we couldseparate the things that are used forpreparing food.

Let us be a little more systematic.List all objects collected, in Table 4.1.Try to identify the materials that eachone is made of. It would be fun tomake this a large table – collectinginformation about as many objectsas possible. It may seem difficult tofind out the materials out of whichsome of these objects are made. Insuch cases, discuss with yourfriends, teacher and parents toidentify the materials.

Table 4.1 Objects and thematerials they are made of

stcejbO erayehtslairetaMfoedam

(etalP ilaht ) scitsalp,ssalg,leetS)rehtoyna(

neP latem,scitsalP

Activity 2

Table 4.2 lists some commonmaterials. You can also add morematerials in Column 1 that areknown to you. Now, try and think ofeveryday objects you know, that aremade mainly of these materials, andlist them in Column 2.

Table 4.2 Different types ofobjects that are made from the

same material

lairetaM foedamstcejbOslairetameseht

dooW,elbat,riahC

trackcollub,hguolp...,sleehwstidna

repaP,skoobeton,skooB

,syot,repapswen...,sradnelac

rehtaeL

scitsalP

nottoC

What do we find from thesetables? First, we grouped objects inmany different ways. We then found

28 SCIENCE

that objects around us are made ofdifferent materials. At times, anobject is made of a single material.An object could also be made of manymaterials. And then again, onematerial could be used for makingmany different objects. What decideswhich material should be used formaking any given object? It seemsthat we need to know more aboutdifferent materials.

4.2 PROPERTIES OF MATERIALS

Have you ever wondered why atumbler is not made with a piece ofcloth? Recall our experiments withpieces of cloth in Chapter 3 and alsokeep in mind that we generally usea tumbler to keep a liquid. Therefore,would it not be silly, if we were tomake a tumbler out of cloth (Fig 4.2)!What we need for a tumbler is glass,plastics, metal or other such materialthat will hold water. Similarly, itwould not be wise to use paper-likematerials for cooking vessels.

We see then, that we choose amaterial to make an object depending

for their usage? Some properties arediscussed here.

AppearanceMaterials usually look different fromeach other. Wood looks very differentfrom iron. Iron appears different fromcopper or aluminium. At the sametime, there may be some similaritiesbetween iron, copper and aluminiumthat are not there in wood.

Activity 3Collect small pieces of differentmaterials – paper, cardboard, wood,copper wire, aluminium sheet, chalk.Do any of these appear shiny?Separate the shiny materials into agroup.

Now, observe as the teacher cutseach material into two pieces andlook at the freshly cut surface(Fig. 4.3). What do you notice? Doesthe freshly cut surface of some ofthese materials appear shiny ?Include these objects also in thegroup of shiny materials.

Do you notice such a shine orlustre in the other materials, cutthem anyway as you can? Repeat thisin the class with as many materialsas possible and make a list of thosewith and without lustre. Instead ofcutting, you can rub the surface ofmaterial with sand paper to see if ithas lustre.

Fig. 4.2 Using a cloth tumbleron its properties, and the purposefor which the object is to be used.

So, what are all the properties ofmaterials that would be important

Fig. 4.3 Cutting pieces of materials to seeif they have lustre


Materials that have such lustreare usually metals. Iron, copper,aluminium and gold are examplesof metals. Some metals often losetheir shine and appear dull, becauseof the action of air and moisture onthem. We therefore, notice the lustre,only on their freshly cut surface.When you visit an ironsmith or aworkshop, look out for freshly cutsurfaces of metal rods to see if theyhave lustre.

HardnessWhen you press different materialswith your hands, some of them maybe hard to compress while others canbe easily compressed. Take a metalkey and try to scratch with it, thesurface of a piece of wood,aluminium, a piece of stone, a nail,candle, chalk, any other material orobject. You can easily scratch somematerials, while some cannot bescratched so easily. Materials whichcan be compressed or scratchedeasily are called soft while some othermaterials which are difficult tocompress are called hard. Forexample, cotton or sponge is softwhile iron is hard.

In appearance, materials can havedifferent properties, like lustre,hardness, be rough or smooth. Canyou think of other properties thatdescribe the appearance of amaterial?

Soluble or Insoluble?Activity 4Collect samples of some solidsubstances such as sugar, salt, chalkpowder, sand and sawdust. Take fiveglasses or beakers. Fill each one of

them about two-thirds with water.Add a small amount (spoonful) ofsugar to the first glass, salt to thesecond and similarly, add smallamounts of the other substances intothe other glasses. Stir the contentsof each of them with a spoon. Waitfor a few minutes. Observe whathappens to the substances added towater (Fig. 4.4). Note yourobservations as shown in Table 4.3.

Table 4.3 Mixing different solidmaterials in water

ecnatsbuS /retawnisraeppasiDraeppasidtonseod

tlaS niyletelpmocsraeppasiDretaw

raguS

dnaS

klahCredwop

tsudwaS

You will notice that somesubstances have completely disappe-ared or dissolved in water. We saythat these substances are soluble inwater. Other substances do not mixwith water and do not disappear evenafter we stir for a long time. Thesesubstances are insoluble in water.

Fig. 4.4 What disappears, what doesn’t?

30 SCIENCE

Water plays an important role inthe functioning of our body becauseit can dissolve a large number ofsubstances. Do liquids also dissolvein water?

Activity 5Collect samples of vinegar, lemonjuice, mustard oil or coconut oil,kerosene or any other liquid. Take aglass tumbler. Fill it up to half withwater. Add a few spoonfuls of oneliquid to this and stir it well. Let itstand for five minutes. Observewhether the liquid mixes with water(Fig. 4.5). Repeat the same with otherliquids, as many different liquids asare available to you. Write yourobservations in Table 4.4.

Table 4.4 Solubility of somecommon liquids in water

diuqiL /llewsexiMximtonseoD

rageniV llewsexiM

eciujnomeL

liodratsuM

liotunocoC

enesoreK

We notice that some liquids getcompletely mixed with water. Someothers do not mix with water andform a separate layer when kept asidefor some time.

Some gases are soluble in waterwhereas others are not. Water,usually, has small quantities of somegases dissolved in it. For example,oxygen gas dissolved in water is veryimportant for the survival of animalsand plants that live in water.

Objects may float or sink inwaterWhile doing Activity 4, you mighthave noticed that the insoluble solidsseparated out from water. You mayhave also noticed this with someliquids in Activity 5. Some of thesematerials that did not mix with water,floated to the surface of water. Othersmay have sunk to the bottom of thetumbler, right? We notice manyexamples of objects that float in wateror sink (Fig. 4.6). Dried leaves fallenon the surface of a pond, a stone thatyou throw into this pond, few dropsof honey that you let fall into a glassof water. What happens to allof these?

Fig. 4.5 (a) Some liquids mix well withwater while (b) some others do not

(a) (b)

Boojho suggests that wealso check if the liquids that weused in Activity 5, mix well withsome liquid other than water.

Paheli is curious to knowwhether gases also dissolvein water.


Boojho would like you to give himfive examples each, of objects thatfloat and those that sink in water.What about testing these samematerials to see if they float or sinkin other liquids like oil?

TransparencyYou might have played the game ofhide and seek. Think of some placeswhere you would like to hide so thatyou are not seen by others. Why didyou choose those places? Would youhave tried to hide behind a glasswindow? Obviously not, as yourfriends can see through that and

spot you. Can you see through allthe materials? Those substances ormaterials, through which things canbe seen, are called transparent(Fig. 4.7). Glass, water, air and someplastics are examples of transparentmaterials. Shopkeepers usuallyprefer to keep biscuits, sweets andother eatables in transparentcontainers of glass or plastic, so thatbuyers can easily see these items(Fig. 4.8).

On the other hand, there are somematerials through which you are notable to see. These materials are calledopaque. You cannot tell what is keptin a closed wooden box, a cardboardcarton or a metal container. Wood,cardboard and metals, are examplesof opaque materials.

Do we find that we can group allmaterials and objects, without anyconfusion, as either opaque ortransparent?

Activity 6

Take a sheet of paper and lookthrough it towards a lighted bulb.Make a note of your observation.Now, put 2-3 drops of some oil andspread it on the sheet of paper. Lookagain towards the lighted bulbthrough that portion of the paper on

Fig. 4.7 Looking through opaque,transparent or translucent material

Figure 4.6 Some objects float in water whileothers sink in it

Fig. 4.8 Transparent bottles in a shop

32 SCIENCE

which the oil has been spread. Doyou find that the bulb is more clearlyvisible than before? But, can yousee clearly through the oiled paper?Is everything on the other side of itvisible? Perhaps not. The materialsthrough which objects can be seen,but not clearly, are known astranslucent. Remember the oilypatch on paper when we tested fooditems for presence of fats? That wastranslucent too! Can you think ofsome more examples of translucentmaterials?

We can therefore group materialsas opaque, transparent and trans-lucent.

Paheli suggestscovering the glassof a torch withyour palm at adark place. Switchon the torch andobserve the otherside of the palm.She wants toknow whether

palm of your hand is opaque,transparent or translucent?

We learnt that materials differ intheir appearance and the way theymix in water or other liquids. Theymay float or sink in water or may betransparent, opaque or translucent.Materials can be grouped on thebasis of similarities or differences intheir properties.

Why do we need to groupmaterials? In everyday life, we oftengroup materials for our convenience.At home, we usually store things insuch a manner that similar objectsare placed together. Such anarrangement helps us to locate themeasily. Similarly, a grocer usuallykeeps all type of biscuits at onecorner of his shop, all soaps atanother while grains and pulses arestored at some other place.

There is another reason why wefind such grouping useful. Dividingmaterials in groups makes itconvenient to study their propertiesand also observe any patterns inthese properties. We will study moreabout this in higher classes.

Fig. 4.9 Does torchlight pass through

your palm?

draH

elbulosnI

ertsuL

lairetaM

slateM

euqapO

hguoR

elbuloS

tneculsnarT

tnerapsnarT

Key Words


Objects around us are made up of a large variety of materials.

A given material could be used to make a large number of objects. It isalso possible that an object could be made of a single material or of manydifferent types of materials.

Different types of materials have different properties.

Some materials are shiny in appearance while others are not. Some arerough, some smooth. Similarly, some materials are hard, whereas someothers are soft.

Some materials are soluble in water whereas some others are insoluble.

Some materials such as glass, are transparent and some others such aswood and metals are opaque. Some materials are translucent.

Materials are grouped together on the basis of similarities and differencesin their properties.

1. Name five objects which can be made from wood.

2. Select those objects from the following which shine:Glass bowl, plastic toy, steel spoon, cotton shirt

3. Match the objects given below with the materials from which they could bemade. Remember, an object could be made from more than one material anda given material could be used for making many objects.

stcejbO slairetaM

kooB ssalG

relbmuT dooW

riahC repaP

yoT rehtaeL

seohS scitsalP

4. State whether the statements given below are True or False.(i) Stone is transparent, while glass is opaque.(ii) A notebook has lustre while eraser does not.(iii) Chalk dissolves in water.(iv) A piece of wood floats on water.

Summary

Exercises

34 SCIENCE

SUGGESTED ACTIVITY

1. You may have played a memory game with your friends. Several objects areplaced on a table, you are asked to observe them for a few minutes, go intoanother room and write down the names of all objects that you can remem-ber. Play this game, with a difference! Ask all the participants in the game toremember objects with some particular property while playing this memorygame — remember and write down the names of objects that were made ofwood or objects that are edible and so on. Have fun!

2. From a large collection of materials, make groups of objects having differentproperties like transparency, solubility in water and other properties. Inlater chapters you will also learn about properties of materials related toelectricity and magnetism. After making different groups from the collectedmaterials, try and find out if there are any patterns in these groups. Forinstance, do all materials which have lustre conduct electricity?

(v) Sugar does not dissolve in water.

(vi) Oil mixes with water.

(vii) Sand settles down in water.

(viii) Vinegar dissolves in water.

5. Given below are the names of some objects and materials:

Water, basket ball, orange, sugar, globe, apple and earthen pitcher

Group them as:

(a) Round shaped and other shapes

(b) Eatables and non eatables

6. List all items known to you that float on water. Check and see if they will floaton an oil or kerosene.

7. Find the odd one out from the following:

a) Chair, Bed, Table, Baby, Cupboard

b) Rose, Jasmine, Boat, Marigold, Lotus

c) Aluminium, Iron, Copper, Silver, Sand

d) Sugar, Salt, Sand, Copper sulphate

Separation of Substances5

Seems easy, but what if thematerials we want to separate aremuch smaller than mango or guava?Imagine you are given a glass of sandwith salt mixed in it. Impossible, evento think of separating salt from thismixture by picking out grains of sandby hand!

Activity 1

In Column 1 of Table 5.1, are givena few processes of separation. Thepurpose of separation and the wayseparated components are used is

Fig. 5.1 Separating tea leaves with astrainer

There are many instances whenwe notice a substance beingseparated from a mixture

of materials.Tea leaves are separated from the

liquid with a strainer, while preparingtea (Fig. 5.1).

Grain is separated from stalks,while harvesting. Milk or curd ischurned to separate the butter(Fig. 5.2). As we learned in Chapter3, we gin cotton to separate its seedsfrom the fibre.

Perhaps youmight have eatensalted daliya orpoha. If you foundthat it had chillies

in it, you may have carefully takenthem out before eating.

Suppose you are given a basketcontaining mangoes and guavas andasked to separate them. What wouldyou do? Pick out one kind and placethem in a separate container, right?

Fig. 5.2 Butter is taken out by churning milkor curds

But, why would we needto separate substanceslike this at all, is whatPaheli wants to know.

36 SCIENCE

mentioned in Column 2 and 3respectively. However, the infor-mation given in Columns 2 and 3 isjumbled up. Can you match eachprocess with its purpose and the wayseparated components are used?

We see that, before we use asubstance, we need to separateharmful or non-useful substancesthat may be mixed with it.Sometimes, we separate even usefulcomponents if we need to use themseparately.

The substances to be separatedmay be particles of different sizes ormaterials. These may be solids,liquids or even gases. So, how do weseparate substances mixed togetherif they have so many differentproperties?5.1 METHODS OF SEPARATION

We will discuss some simple methodsof separating substances that aremixed together. You may come acrosssome of these methods being usedin day to day activities.

Hand PickingActivity 2Bring a packet of grain purchased

from a shop to the classroom. Now,spread the grain on a sheet of paper.Do you find only one kind of grainon the sheet of paper? Are therepieces of stone, husks, broken grainand particles of any other grain init? Now, remove with your hand thepieces of stone, husks and othergrains from it.

This method of handpicking canbe used for separating slightly largersized impurities like the pieces ofdirt, stone, and husk from wheat,rice or pulses (Fig. 5.3). The quantityof such impurities is usually not verylarge. In such situations, we find thathandpicking is a convenient methodof separating substances.

Table 5.1 Why do we separate substances?

noitarapeSssecorp

odewhcihwrofesopruPnoitarapeseht

ehthtiwodewodtahW?stnenopmocdetarapes

etarapeS)1ecirmorfsenots

,tnereffidowtetarapesoT)a.stnenopmoclufesutub

dliosehtyawaworhteW)i.tnenopmoc

klimgninruhC)2rettubniatboot

lufesu-nonevomeroT)b.stnenopmoc

ehtyawaworhteW)ii.seitirupmi

aetetarapeS)3sevael

roseitirupmievomeroT)c.stnenopmoclufmrah

ehthtobesueW)iii.stnenopmoc

Fig. 5.3 Handpicking stones from grain

37SEPARATION OF SUBSTANCES

ThreshingYou must have seen bundles of wheator paddy stalks lying in fields afterharvesting the crop. Stalks are driedin the sun before the grain isseparated from them. Each stalk hasmany grain seeds attached to it.Imagine the number of grain seedsin hundreds of bundles of stalk lyingin the field! How does the farmerseparate grain seeds from thosebundles of stalks?

One may pluck mangoes orguavas from the trees. But, grainseeds are much smaller thanmangoes or guavas. So, pluckingthem from their stalks would beimpossible. How does one separategrain seeds from their stalks?

The process that is used toseparate grain from stalks isthreshing. In this process, the stalksare beaten to free the grain seeds(Fig.5.4).

Winnowing

Activity 3

Make a mixture of dry sand withsawdust or powdered dry leaves. Keepthis mixture on a plate or a news-paper. Look at this mixture carefully.Can the two different components bemade out easily? Are the sizes ofparticles of the two componentssimilar? Would it be possible toseparate the components byhandpicking?

Now, take your mixture to anopen ground and stand on a raisedplatform. Put the mixture in a plateor sheet of paper. Hold the plate orthe sheet of paper containing themixture, at your shoulder height.Tilt it slightly, so that the mixtureslides out slowly.

What happens? Do both thecomponents — sand and sawdust (orpowdered leaves) fall at the sameplace? Is there a component thatblows away? Did the wind manageto separate the two components?

This method of separatingcomponents of a mixture is called

Fig. 5.4 Threshing

Sometimes, threshing is donewith the help of bullocks. Machinesare also used to thresh largequantities of grain. Fig. 5.5 Winnowing

38 SCIENCE

winnowing. Winnowing is used toseparate heavier and lightercomponents of a mixture by wind orby blowing air. This method iscommonly used by farmers toseparate lighter husk particles fromheavier seeds of grain (Fig. 5.5).

The husk particles are carriedaway by the wind. The seeds of grainget separated and form a heap nearthe platform for winnowing. Theseparated husk is used for manypurposes such as fodder for cattles.

SievingSometimes, we may wish to preparea dish with flour. We need to removeimpurities and bran that may bepresent in it. What do we do? We usea sieve and pour the flour into it(Fig. 5.6).

Sieving allows the fine flourparticles to pass through the holesof the sieve while the biggerimpurities remain on the sieve.

In a flour mill, impurities likehusk and stones are removed fromwheat before grinding it. Usually, abagful of wheat is poured on aslanting sieve. The sieving removespieces of stones, stalk and husk thatmay still remain with wheat afterthreshing and winnowing.

You may have also noticed similarsieves being used at construction

Fig. 5.7 Pebbles and stones are removedfrom sand by sieving

Fig. 5.6 Sieving

sites to separate pebbles and stonesfrom sand (Fig. 5.7).

Activity 4

Bring a sieve and a small quantity offlour from home, to the class. Sievethe flour to separate any impuritiesin it. Now, make a fine powder ofchalk pieces and mix it with the flour.Can we separate the flour and thepowdered chalk by sieving?

Sieving is used when componentsof a mixture have different sizes.

Sedimentation, Decantationand FiltrationSometimes, it may not be possibleto separate components of a mixtureby winnowing and handpicking. Forexample, there may be lighterimpurities like dust or soil particlesin rice or pulses. How are suchimpurities separated from rice orpulses before cooking?

Rice or pulses are usually washedbefore cooking. When you add water


to these, the impurities like dust andsoil particles get separated. Theseimpurities go into water, whichbecomes a little muddy. Now, whatwill sink to the bottom of the vessel— rice or dust? Why? Have you seenthat the vessel is tilted to pour outthe dirty water?

When the heavier component ina mixture settles after water is addedto it, the process is called sedi-mentation. When the water (alongwith the dust) is removed, the processis called decantation (Fig. 5.8). Letus find a few other mixtures that canbe separated through sedimentationand decantation.

The same principle is used forseparating a mixture of two liquidsthat do not mix with each other. Forexample, oil and water from theirmixture can be separated by thisprocess. If a mixture of such liquidsis allowed to stand for some time, theyform two separate layers. Thecomponent that forms the top layercan then be separated by decantation.

Let us again consider a mixure ofa solid and liquid. After preparingtea, what do you do to remove thetea leaves? Try decantation. It helpsa little. But, do you still get a few

leaves in your tea? Now, pour the teathrough a strainer. Did all the tealeaves remain in the strainer? Thisprocess is called filtration (Fig. 5.1).Which method of separating tealeaves from prepared tea is better,decantation or filtration?

Let us now consider the exampleof water that we use. Do all of us, atall times, get safe water to drink?Sometimes, water supplied throughtaps may be muddy. The watercollected from ponds or rivers mayalso be muddy, especially after rains.Let us see if we can use some methodof separation to remove insolubleimpurities like soil from the water.

Activity 5

Collect some muddy water from apond or a river. If it is not available,mix some soil to water in a glass. Letit stand for half an hour. Observe thewater carefully and note yourobservations.

Does some soil settle at thebottom of water? Why? What will youcall this process?

Now, slightly tilt the glass withoutdisturbing the water. Let the waterfrom the top flow into another glass(Fig. 5.8). What will you call thisprocess?

Is the water in the second glassstill muddy or brown in colour? Nowfilter it. Did the tea strainer work?Let us try filtering the water througha piece of cloth. In a piece of cloth,small holes or pores remain inbetween the woven threads. Thesepores in a cloth can be used as afilter.

Fig. 5.8 Separating two components of amixture by sedimentation and de-cantation

40 SCIENCE

If the water is still muddy,impurities can be separated by a filterthat has even smaller pores. A filterpaper is one such filter that has veryfine pores in it. Fig. 5.9 shows thesteps involved in using a filter paper.A filter paper folded in the form of acone is fixed onto a funnel (Fig. 5.10).The mixture is then poured on thefilter paper. Solid particles in themixture do not pass through it andremain on the filter.

Fruit and vegetable juices areusually filtered before drinking toseparate the seeds and solid particlesof pulp. The method of filtration isalso used in the process of preparingcottage cheese (paneer) in our homes.You might have seen that for makingpaneer, a few drops of lemon juiceare added to milk as it boils. Thisgives a mixture of particles of solidpaneer and a liquid. The paneer isthen separated by filtering themixture through a fine cloth or astrainer.

Evaporation

Activity 6Heat a beaker containing some water.Allow the water to boil. If youcontinue heating, would the waterturn into steam and disappearcompletely? Now, add two spoons of

Fig. 5.9 Folding a filterpaper to make a cone

Fig. 5.10 Filtrationusing a filter paper

Fig. 5.11 Heating a beaker containing saltwater

salt to water in another beaker andstir it well. Do you see any changein the colour of water? Can you seeany salt in the beaker, after stirring?Heat the beaker containing the saltwater (Fig. 5.11). Let the water boilaway. What is left in the beaker ?

In this activity, we used theprocess of evaporation, to separate amixture of water and salt.

The process of conversion of waterinto its vapour is called evaporation.The process of evaporation takesplace continuously wherever wateris present.

Where do you think, salt comesfrom? Sea water contains many saltsmixed in it. One of these salts is the


common salt. When sea water isallowed to stand in shallow pits,water gets heated by sunlight andslowly turns into water vapour,through evaporation. In a few days,the water evaporates completelyleaving behind the solid salts (Fig.5.12). Common salt is then obtainedfrom this mixture of salts by furtherpurification.

Use of more than one methodof separationWe have studied some methods forseparation of substances from theirmixtures. Often, one method is notsufficient to separate the differentsubstances present in a mixture. Insuch a situation, we need to usemore than one of these methods.

Activity 7Take a mixture of sand and salt. Howwill we separate these? We alreadysaw that handpicking would not bea practical method for separatingthese.

Keep this mixture in a beaker andadd some water to this. Leave thebeaker aside for some time. Do yousee the sand settling down at thebottom? The sand can be separatedby decantation or filtration. Whatdoes the decanted liquid contain?Do you think this water contains the

salt which was there in the mixtureat the beginning?

Now, we need to separate salt andwater from the decanted liquid.Transfer this liquid to a kettle andclose its lid. Heat the kettle for sometime. Do you notice steam comingout from the spout of the kettle?

Take a metal plate with some iceon it. Hold the plate just above thespout of the kettle as shown inFig. 5.13. What do you observe? Letall the water in the kettle boil off.

When the steam comes in contactwith the metal plate cooled with ice,it condenses and forms liquid water.The water drops that you observedfalling from the plate, were due tocondensation of steam. The processof conversion of water vapour into itsliquid form is called condensation.

Did you ever see water dropscondensed under a plate that hasbeen used to cover a vesselcontaining milk that has just beenboiled?

After all the water has evaporated,what is left behind in the kettle?

We have thus, separated salt,sand and water using processes ofdecantation, filtration, evaporationand condensation.

Paheli faced a problem whilerecovering salt mixed with sand. Shehas mixed a packet of salt in a small

Fig. 5.12 Obtaining salt from sea water

Fig. 5.13 Evaporation and condensation

42 SCIENCE

amount of sand. She then tried themethod suggested in Activity 7, torecover the salt. She found, however,that she could recover only a smallpart of the salt that she had taken.What could have gone wrong ?

Can water dissolve anyamount of a substance?In chapter 4, we found that manysubstances dissolve in water andform a solution. We say that thesesubstances are soluble in water. Whatwill happen if we go on adding moreand more of these substances to afixed quantity of water?

Activity 8

You will need a beaker or a smallpan, a spoon, salt and water. Pourhalf a cup of water in the beaker. Addone teaspoonful of salt and stir itwell, until the salt dissolvescompletely (Fig 5.14). Again add ateaspoonful of salt and stir well. Goon adding salt, one teaspoonful at atime, and stir.

After adding a few spoons of salt,do you find that some salt remainsundissolved and settles at the bottomof the beaker? If yes, this means thatno more salt can be dissolved in theamount of water we have taken. Thesolution is now said to be saturated.

Here is a hint as to what mighthave gone wrong when Paheli triedto recover large quantity of salt mixedwith sand. Perhaps the quantity ofsalt was much more than thatrequired to form a saturated solution.The undissolved salt would have

remained mixed with the sand andcould not be recovered. She couldsolve her problem by using a largerquantity of water.

Suppose, she did not havesufficient quantity of water to dissolveall the salt in the mixture. Is theresome way that water could be madeto dissolve more salt before thesolution gets saturated?

Let us try and help Paheli out.

Activity 9

Take some water in a beaker and mixsalt in it until it cannot dissolve anymore salt. This will give you asaturated solution of salt in water.

Now, add a small quantity of saltto this saturated solution and heatit. What do you find? What happensto the undissolved salt in the bottomof the beaker? Does it dissolve, now?If yes, can some more salt bedissolved in this solution by heatingit?

Let this hot solution cool. Doesthe salt appear to settle at the bottomof the beaker again?

The activity suggest that largerquantity of salt can be dissolved inwater on heating.

Fig 5.14 Dissolving salt in water


Does water dissolve equalamounts of different solublesubstances? Let us find out.

Activity 10

Take two glasses and pour half a cupof water in each of them. Add ateaspoon of salt to one glass and stirtill the salt dissolves. Go on addingsalt, one teaspoon at a time, till thesolution saturates. Record thenumber of spoons of salt thatdissolved in the water, in Table 5.2.Now, repeat the same activity withsugar. Repeat this with some othersubstances that are soluble in water.

What do you notice fromTable 5.2? Do you find that waterdissolves different substances indifferent amounts?

Table 5.2

ecnatsbuSfosnoopsforebmuN

tahtecnatsbusretawnidevlossid

tlaS

raguS

We have discussed a few methodsof separating substances. Some ofthe methods of separation presentedin this chapter are also used in ascience laboratory.

We also learnt that a solution isprepared by dissolving a substancein a liquid. A solution is said to besaturated if it cannot dissolve moreof the substance in it.

gninruhC

noitasnednoC

noitatnaceD

noitaropavE

noitartliF

gnikcipdnaH

noitulosdetarutaS

noitatnemideS

gniveiS

noituloS

gnihserhT

gniwonniW

Handpicking, winnowing, sieving, sedimentation, decantation andfiltration are some of the methods of separating substances from theirmixtures.

Summary

Key Words

44 SCIENCE

1. Why do we need to separate different components of a mixture? Give two ex-amples.

2. What is winnowing? Where is it used?

3. How will you separate husk or dirt particles from a given sample of pulses be-fore cooking.

4. What is sieving? Where is it used?

5. How will you separate sand and water from their mixture?

6. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?

7. How would you obtain clear water from a sample of muddy water?

8. Fill up the blanks

(a) The method of separating seeds of paddy from its stalks is called ___________.

(b) When milk, cooled after boiling, is poured onto a piece of cloth the cream(malai) is left behind on it. This process of separating cream from milk isan example of ___________.

(c) Salt is obtained from seawater by the process of ___________.

(d) Impurities settled at the bottom when muddy water was kept overnight ina bucket. The clear water was then poured off from the top. The process ofseparation used in this example is called ___________.

9. True or false?(a) A mixture of milk and water can be separated by filtration.

(b) A mixture of powdered salt and sugar can be separated by the process ofwinnowing.

Husk and stones could be separated from grains by handpicking.

Husk is separated from heavier seeds of grain by winnowing.

Difference in the size of particles in a mixture is utilised to separate themby the process of sieving and filtration.

In a mixture of sand and water, the heavier sand particles settle down atthe bottom and the water can be separated by decantation.

Filtration can be used to separate components of a mixture of an insolublesolid and a liquid.

Evaporation is the process in which a liquid gets converted into its vapour.Evaporation can be used to separate a solid dissolved in a liquid.

A saturated solution is one in which no more of that substance can bedissolved.

More of a substance can be dissolved in a solution by heating it.

Water dissolves different amount of soluble substances in it.

Exercises



1. Visit a nearby dairy and report about the processes used to separate creamfrom milk.

2. You have tried a number of methods to separate impurities like mud fromwater. Sometimes, the water obtained after employing all these processescould still be a little muddy. Let us see if we can remove even this impuritycompletely. Take this filtered water in a glass. Tie a thread to a small piece ofalum. Suspend the piece of alum in the water and swirl. Did the water be-come clear? What happened to the mud? This process is called loading. Talkto some elders in your family to find out whether they have seen or used thisprocess.

(c) Separation of sugar from tea can be done with filtration.

(d) Grain and husk can be separated with the process of decantation.

10. Lemonade is prepared by mixing lemon juice and sugar in water. You wish toadd ice to cool it. Should you add ice to the lemonade before or after dissolv-ing sugar? In which case would it be possible to dissolve more sugar?

THINGS TO SEE

“The winnowers”, painted by Gustav Courbet in 1853

Reproduced with permission from Museè de Beaus Arts, Nantes, France

Fig 6.1 A balloon changes its size andshape on blowing air into it

Changes Around us6What fun if you suddenly get

some magical powers tochange anything around

you! What are the things you wouldwant to change?

We do not have magical powers,of course. But, we can still change afew things around us, perhaps manythings. Can you list a few things youcan change around you, with nomagic involved?

Many changes are taking placearound us on their own. In the fields,the crops change from time to time.Sometimes, leaves fall from trees,change colour and dry out. Theflowers bloom and then wither away.Are any changes happening in yourbody? Your nails grow, your hairgrows, you grow taller and yourweight increases as you grow. Didyou realise earlier that so manychanges are taking place around youall the time?

Can some of the changes begrouped together?

How can we group variouschanges? It might help, if we findsome similarities between them.

6.1 CAN ALL CHANGES ALWAYS BE

REVERSED?

Activity 1

Take a balloon and blow it. Take carethat it does not burst. The shape andsize of the balloon have changed(Fig. 6.1). Now, let the air escape theballoon.

Activity 2Take a piece of paper and fold it asshown in Fig.6.2. You have changedthe sheet of paper into a toyaeroplane. You may have lots of funin flying this plane. Once you aretired of it, unfold the paper again.

47CHANGES AROUND US

Activity 3

Take some dough and make a ball.Try to roll out a roti (Fig. 6.3). Maybe you are not happy with its shapeand wish to change it back into aball of dough again.

Now, think about the threechanges you observed in Activity 1,2 and 3. What do they have incommon?

Was it possible to get the balloonback to its original shape and size?

Was the size of the paper same asbefore and after making anaeroplane?

Was it possible to get back the ballof dough again?

What do you conclude? In eachof the three activities, is it possibleto get back to the material with whichwe started our activity? If the answeris yes, it means that the changesoccurring in these activities can bereversed. Now, let us repeat the sameactivities with a difference.

Fig 6.2 A toy aeroplane made by foldingpaper

Fig 6.3 A ball of dough and a rolled out roti

Fig. 6.4 An aeroplane cut out of paper

Fig 6.5 A roti

Activity 4

Take the same balloon, which youused in Activity 1. Blow it to its fullsize and tie its mouth with a stringtightly. Prick it with the pointed tipof your pencil. Oops! It burst.

Activity 5

Take the same piece of paper, whichyou used in Activity 2. Draw anaeroplane on it and cut along itsoutline (Fig.6.4).

Activity 6

Roll out a roti from the ball of doughagain and bake it on a tawa (Fig.6.5).

Suppose, you are asked the samethree questions which you answeredafter Activity 3. What would youranswers be, now?

We see that, the changes whichhave occurred in the Activity 4, 5 and6 can not be reversed.

You use a pencil and an eraser.With repeated use, their shape andsize changes. Can we reverse this

48 SCIENCE

change? You must have seen a potterworking on his wheel. He shapes alump of clay into a pot. Can thischange be reversed? He then bakesthe pot in an oven. Now, can thischange be reversed?

Table 6.1 Some common changes

egnahC ebnaCdesreveR

ggedeliobotggewaR oN/seY

ildiotrettaB

sehtolcyrdotsehtolcteW

dettinkotnraynellooWretaews

ruolfstiotniarG

klimtohotklimdloC

liocotgnirtsthgiartSgnirts

rewolfotduB

otkliM reenap

sagoibotgnudwoC

otdnabrebburdehctertSezislamronsti

netlomotmaercecidiloSmaerceci

Some common changes are givenin Table 6.1. Which of these changes,do you think can be reversed?

We find that one way we cangroup changes is to see if they canbe reversed.

6.2 COULD THERE BE OTHERWAYS TO BRING A CHANGE?

We all have seen the tools which areused to dig the soil (Fig. 6.6 ). Haveyou ever seen how the iron blade inthese tools is fixed to the woodenhandle?

Fig. 6.6 Tools are often heated beforefixing wooden handles

The iron blade of these tools hasa ring in which the wooden handleis fixed. Normally, the ring is slightlysmaller in size than the woodenhandle. To fix the handle, the ring isheated and it becomes slightly largerin size (expands). Now, the handleeasily fits into the ring. When the ringcools down it contracts and fitstightly on to the handle.

Such a change is also used forfixing the metal rim on a woodenwheel of a cart as shown in Fig.6.7.Again the metal rim is made slightlysmaller than the wooden wheel. Onheating, the rim expands and fitsonto the wheel. Cold water is thenpoured over the rim, which contractsand fits tightly onto the wheel.

49CHANGES AROUND US

Fig. 6.7 Cart wheel with metal rim fixed toit

When we heat water in a pan, itbegins to boil after some time. If wecontinue to heat further, the quantityof water in the pan begins to decrease.

The water changes into its vapour.In Activity 7, Chapter 5 you haveobserved that water vapour getschanged into liquid water when it iscooled. We all have noticed melting ofice. Ice melts when it is heated. Whatdoes it change into? Is it possible tochange this water back into ice?

Let us observe some more changes.

Paheli wants to know ifyou have ever seen ablacksmith making sometools. How does ablacksmith change a

piece of iron into different tools? Apiece of iron is heated till it becomesred-hot. It then becomes soft andis beaten into a desired shape. Whatchange has taken place in iron, onbeing heated?

Boojho has often noticed that roadconstruction workers heat a blackmaterial (tar) for repairing a road.He wants to know whether thechange caused in tar, by heating,

is reversible?

Activity 7

Take a small candle and measure itslength with a scale. Now, fix it at asuitable place and light it. Let it burnfor some time. Now blow out thecandle and measure its length again(Fig.6.8).

Can the change in the length ofthe candle be reversed? If we were totake some wax in a pan and heat it,can this change be reversed(Fig. 6.9)?

Fig.6.8 Burning of acandle

Fig.6.9 Heating wax

50 SCIENCE

Repeat Activity 7 with an incensestick. Wait till it burns awaycompletely. What are the changesthat occur in the incense stick? Thestick burns to produce some newmaterial. These are ash and somegases. We cannot see these gases butcan sense them due to their pleasantsmell. Can this change be reversed?And what about the change, whichoccurred in the matchstick you usedfor lighting the candle or incensestick?

So far we have discussed thechanges occurring in a given objector its material. What about thechanges that occur when twosubstances are mixed together?

In Chapter 4, we dissolved salt inwater. Do you think a changeoccured in salt or in water? Is itpossible to reverse this change? Wait,in Chapter 5, we learnt how toseparate salt from its solution inwater. So, can we say that the change

due to dissolving salt in water bereversed?

Paheli asks if you have ever seencurd being set. A small quantity ofcurd is added to warm milk. The milkis stirred and is set aside for a fewhours at a warm place. In a fewhours, the milk changes into curd.Can this change be reversed?

We find that a few ways to bringabout a change in a substance couldbe, by heating it or by mixing it withsome other substance. We also findthat some changes can be reversed,while some others cannot bereversed. There must be many otherways of changing things around us.It is possible that some of them couldbe reversed. Thus, changes aroundus could be grouped as those thatcan be reversed or cannot bereversed. In higher classes, you willlearn more about the ways in whichchanges can be made and the waythese can be grouped.

segnahC

noitcartnoC

noitaropavE

noisnapxE

gnitleM

Some changes can be reversed and some cannot be reversed.

A change may occur by heating a substance or by mixing it with someother.

Summary

Key Words

51CHANGES AROUND US

1. To walk through a waterlogged area, you usually shorten the length of yourdress by folding it. Can this change be reversed?

2. You accidentally dropped your favourite toy and broke it. This is a change youdid not want. Can this change be reversed?

3. Some changes are listed in the following table. For each change, write in theblank column, whether the change can be reversed or not.

.oN.S egnahC )oN/seY(desreverebnaC

.1 doowfoeceipafogniwasehT

.2 ydnacecifognitlemehT

.3 retawniragusgnivlossiD

.4 dooffognikoocehT

.5 ognamafogninepirehT

.6 klimfogniruoS

4. A drawing sheet changes when you draw a picture on it. Can you reverse thischange?

5. Give examples to explain the difference between changes that can or cannotbe reversed.

6. A thick coating of a paste of Plaster of Paris (POP) is applied over the bandageon a fractured bone. It becomes hard on drying to keep the fractured boneimmobilised. Can the change in POP be reversed?

7. A bag of cement lying in the open gets wet due to rain during the night. Thenext day the sun shines brightly. Do you think the changes, which have oc-curred in the cement, could be reversed?


1. Take a lemon, a paintbrush and a piece of paper. Cut the lemon and squeezeout its juice in a cup. Dip the brush in the lemon juice and write a messageon the paper. Let the paper dry and you find that the letters of your messagebecome invisible. Now, press the paper with hot iron or warm it by holdingit above the flame of a candle (Take care that it does not catch fire). As thepaper gets warm, invisible letters change into dark brown colour. Identifythe changes that can be reversed.

2. Observe preparation of dishes at your home. Identify two changes that canbe reversed.

3. Maintain a record for one year of the seasonal changes in vegetables,clothing, nature and events around you. Identify the changes that can orcannot be reversed.

Exercises

Getting to Know Plants7Go outside and observe all the

plants around you. Do yousee that some plants are

small, some very big, while some arejust patches of greenon the soil? Somehave green leaves,while some othershave reddish ones.Some have huge redflowers, some havetiny blue ones, whilesome have none. Wedo see a variety ofplants existing allaround us — near ourhomes, in the schoolground, on the way tothe school, in theparks and gardens, isn’t it?

Let us get to know the differentparts of any plant. This will helpus to understand the differencesbetween plants of different kinds.

Can you label the stem, branches,roots, leaves, and flowers of the plantshown in Fig. 7.1? Colour the partsof the plant.

Let us now go on a Nature walk,

Fig. 7.2 A Nature walk!

Fig. 7.1 Parts of a plant

make friends with many differentkinds of plants and examine themclosely (Fig. 7.2).

7.1 HERBS, SHRUBS AND TREES

Activity 1

Look closely at the stem andbranches of:1. Plants much smaller than you.2. Plants that are about your size,

and3. Plants which are much taller than

you.Feel their stem and try to bend

them gently to see if they are tenderor hard. Take care that the stem does

53GETTING TO KNOW PLANTS

Table 7.1 Categories of plants

tnalPeman

1nmuloCthgieH

nmuloC4

neerG redneT kcihT draH esabehttAmetsehtfo

purehgiHehtno

mets

yrogetaCtnalpfo

otamoT retrohSemnaht seY seY breH

ognaMhcuMrellat

emnahtseY seY seY eerT

nomeLylthgilS

rellatemnaht

seY seY burhS

Column 2Stem

Column 3Where do the

branches appear

not break. Hug the tall plants to seehow thick their stems are!

We also need to notice from wherethe branches grow in some plants —close to the ground or higher up onthe stem.

We will now group all the plantswe observed, in Table 7.1. Someexamples are shown. You can fill theColumns 1, 2 and 3 for many more

Suggestion: Work in groups of4-5 students in doing activitiessuggested in this Chapter so thata minimum number of plants areuprooted.

Use weeds with soft stems forthe activities. Do you know whatweeds are? In crop fields, lawns,or in pots, often some unwantedplants or weeds start growing.Have you seen farmers removingthese weeds from their fields?

plants. Fill Column 4 after you havestudied later part of this section.

Based on these characters mostplants can be classified into threecategories: herbs, shrubs and trees.An example of each is shown inFig.7.3.

Fig.7.3 (a) Herb, (b) shrub and (c) tree(b)

(a)

(c)

54 SCIENCE

Plants with green and tenderstems are called herbs. They areusually short and may not havemany branches [Fig.7.3 (a)].

Some plants have the stembranching out near the base. Thestem is hard but not very thick. Suchplants are called shrubs [Fig .7.3(b)].

Some plants are very tall andhave hard and thick brown stem.The stems have branches in theupper part, much above the ground.Such plants are called trees[Fig.7.3(c)].

Based on the above characteristicscan you now correctly classify theplants listed by you and completecolumn 4 in Table 7.1?

Perhaps there are some plants inyour school or at home that you takecare of. Write down the names of anytwo trees, shrubs, herbs or creepersgrowing in your house or school.

7.2 STEM

Activity 2We would require a glass, water, redink, a herb, and a blade for thisactivity.

Pour water to fill one-third of theglass. Add a few drops of red ink tothe water. Cut the base of the stemof the herb and put it in the glass asshown in Fig.7.5. Observe it the nextday.

Paheli wonders what kind of stem — themoney plant, beanstalk, gourd plants andgrape vines have. Do observe some of theseplants. How are these different from a herb,

a shrub or a tree? Why do you thinksome of them need support to climbupwards?

Fig. 7.4Climbers

Plants with weakstems that cannot standupright and spread onthe ground are calledcreepers, while thosethat take support onneighbouring structuresand climb up are calledclimbers ( Fig.7.4 ).These are different fromthe herbs, shrubs andtrees.

Fig. 7.5 What does the stem do?

Do any of the parts of the herbappear to have red colour? If yes, howdo you think the colour reachedthere?

You can cut the stem across andlook for the red colour inside thestem ( Fig. 7.6) .

From this activity we see thatwater moves up the stem. In otherwords, stem conducts water. Justlike the red ink, minerals dissolvedin water also move up in the stem,along with the water. The water and


7.3 LEAF

Look at leaves of plants around youand draw them in your notebook.Are all the leaves the same in size,shape and colour?

How are they attached to thestem? The part of a leaf by which itis attached to the stem is calledpetiole. The broad, green part of theleaf is called lamina (Fig. 7.8). Canyou identify these parts of the leavesin plants around you? Do all theleaves have petioles?

(a) (b)

Fig. 7.6 (a) Cutting the stem, (b) its enlargedview

C. She wants you to guess whatwould happen to the flower in glassA and the flower put jointly in B andC.

When you had cut across thestem in Activity 2, did you notice anumber of spots of red colourarranged in a ring inside the stem?Does this explain the results thatPaheli obtained? Try this activityyourself !

PetioleLamina

Fig. 7.8 A leaf

Let us get to know the leaf betterby taking its impression! If youthought that leaves cannot sign, hereis an activity which will make youthink again.

Activity 3

Put a leaf under a white sheet of paperor a sheet in your notebook. Hold it inplace as shown in Fig. 7.9. Hold yourpencil tip sideways and rub it on theportion of the paper having the leafbelow it. Did you get an impressionwith some lines in it?Are they similar tothose on the leaf ?These lines on theleaf are calledveins. Do you seea thick vein in themiddle of theleaf?

Fig. 7.9 Taking animpression of a leaf

minerals go to leaves and other plantparts attached to the stem, throughnarrow tubes inside the stem.

Paheli did this activity with herbshaving white flowers. She put onebranch with a white flower in thewater in glass A and added a fewdrops of red ink to the water. Shedid a funny thing with anotherbranch. She split it half way alongits length and put the two ends inthe water in glasses B and C(Fig. 7.7). She put a few drops of red

Fig. 7.7 Paheli’s flowers

AB C

ink in glass B and blue ink in glass

56 SCIENCE

This vein is called the midrib. Thedesign made by veins in a leaf is calledthe leaf venation. If this design isnet-like on both sides of midrib, thevenation is reticulate [Fig. 7.10 (a)].In the leaves of grass you might haveseen that the veins are parallel to oneanother. This is parallel venation[(Fig. 7.10 (b)]. Observe the venationin as many leaves as you can withoutremoving them from the plant. Drawthe pattern and write names of someplants having reticulate and parallelvenation.

Shall we now find out some of thefunctions of a leaf?

Activity 4

We will require a herb, twotransparent polythene bags andsome string.

Do this activity during day timeon a sunny day. Use a healthy, wellwatered plant that has been growingin the sun, for this activity. Enclosea leafy branch of the plant in apolythene bag and tie up its mouthas shown in Fig. 7.11. Tie up themouth of the empty polythene bagand keep it also in the sun.

After a few hours, observe theinner surface of the bags. What doyou see? Are there any droplets ofwater in any of the bags? Which baghas the droplets? How do you thinkthey got there? [Don’t forget toremove the polythene bag after theactivity!]

Water comes out of leaves in theform of vapour by a process calledtranspiration. Plants release a lot ofwater into the air through this process.We will learn more about this inChapter 14.

Why did we tie a bag around theleaves? Would we have seen the waterfrom the transpiration of plantsotherwise? What makes the waterappear on the polythene bag? InChapter 5, we noticed waterchanging into different forms insome of our activities. Can you thinkof these and name the process thatmakes water drops appear on thepolythene bag?

Leaves also have anotherfunction. Let us study this.

Activity 5We would require a leaf, spirit, abeaker, test tube, burner, water, aplate and iodine solution for thisactivity.

Fig. 7.10 Leaf venation (a) reticulate and(b) parallel

(a) (b)

Midrib Veins

Fig. 7.11 What does the leaf do?


Put a leaf in a test tube and pourspirit to completely cover the leaf.Now, put the test tube in a beakerhalf filled with water. Heat the beakertill all the green colour from the leafcomes out into the spirit in the testtube. Take out the leaf carefully andwash it in water. Put it on a plateand pour some iodine solution overit (Fig. 7.12).

How do we know that the leaf hasprepared the starch and not receivedit from another part of the plant? Totest this, the above activity can berepeated with a little difference.

Place a potted plant with greenleaves, in a dark room for a day ortwo. Now, cover a portion of a leaf ofthe plant completely with blackpaper and leave the plant in the Sunfor a day. Remove the leaf covered inblack paper and repeat the test forstarch.

What do you see? Which part ofthe leaf shows the presence of starch?Does this help us understand thatleaves produce starch in the presenceof sunlight?

We see that the stem supplies leafwith water. The leaf uses the waterto make food. The leaves also losewater through transpiration.How dothe stem and leaves get the water?That is where the roots come in!

7.4 ROOT

Look at Fig. 7.13. Who do you thinkis watering their plant correctly,Paheli or Boojho? Why?

Fig. 7.12 What does the leaf contain?

Fig. 7.13 Watering the plants

Note: Since the activity involves theuse of spirit and heating, it isadvised that it is demonstrated bythe teacher in the class.

What do you observe? Compareyour observations with those donein Chapter 2, when you tested foodfor presence of different nutrients.Does this mean that the leaf hasstarch in it?

In Chapter 2, we saw that a sliceof raw potato also shows the presenceof starch. Potatoes get this starchfrom other parts of the plant andstore it. However, leaves preparedtheir food in the presence of sunlightand a green coloured substancepresent in them. For this, they usewater and carbon dioxide from air.This process is called photosynt-hesis. Oxygen is given out in thisprocess. The food prepared by leavesultimately gets stored in differentparts of plant as starch.

58 SCIENCE

Activity 7We would require seeds of gram andmaize, cotton wool, katori and somewater.

Take two katoris. Place some wetcotton wool in them. Put 3 or 4seeds of gram in one and maize inthe other. Keep the cotton wet bysprinkling water every day, untilthe sprouts have grown into youngplants. After a week try to separatethe young plants from the cottonwool (Fig. 7.15).

Fig. 7.14 (a) Weed with roots, and(b) without roots

(a) (b)

Both the plants are wateredregularly, but, one is without roots,isn’t it? Does this activity help youunderstand an important function ofthe root?

Let us do an activity to studyanother function of root.

Fig. 7.15 Young plants grown on cottonwool

Was it easy to separate the cottonwool from the roots? Why?

In Activity 6, we could not easilypull out the plants from the soil,right? We dug them out. The rootshelp in holding the plant firmly inthe soil. They are said to anchor theplant to the soil.

You have seen that there aredifferent kinds of stems and leaves.Do the roots also show a variety? Letus find out.

Activity 8Study Fig. 7.16 (a) and (b) carefully. Now,look at the roots of the gram plants youhave pulled out from the cotton wool.Do they look like the roots shown inFig. 7.16 (a) or those in Fig. 7.16 (b)?

Which part of the plant is in thesoil? Let us learn more about thispart from the following activities.

Activity 6You would require two pots, somesoil, khurpi (for digging), blade or apair of scissors and water. Thisactivity is to be done in groups of4-5 students.

Select two weeds of the same kindfrom an open ground and dig themout. Take care that their roots do notbreak. Plant one of the weeds in thesoil in pot A [Fig. 7.14 (a)]. Cut offthe roots from the other weed andplant it in the soil in pot B [Fig. 7.14(b)]. Water them regularly. Observethe plants after a week. Are bothplants healthy?


Fig.7.17 (a), the main root is calledtap root and the smaller roots arecalled lateral roots. Plants with rootsas shown in Fig. 7.17 (b) do not haveany main root. All roots seem similarand these are called fibrous roots.

Separate the weeds you havecollected into (a) those that have taproots and (b) those that have fibrousroots. Look at the leaves of the plantsin Group (a). What kind of venationdo they have? What kind of venationdo you see for plants of Group (b)?

Do you notice that leaf venationand the type of roots in a plant arerelated in a very interesting way? InTable 7.2, can you match the type ofleaf venation and the type of rootsfor some plants you have studied in

Fig 7.16 (a) Roots of_______________

(b) Roots of_______________

(a) (b)

Fig. 7.17 (a) Taproot and (b) fibrous roots(a) (b)

Boojho has a brilliant idea! If hewants to know what kind of rootsa plant has, he need not pull itout. He just has to look at itsleaves!

all the activities so far?

Table 7.2 Types of roots andtypes of leaf venation

foemaNtnalp

faelfoepyTnoitanev

foepyTstoor

We have learnt that roots absorbwater and minerals from the soil andthe stem conducts these to leaves

How about the roots of the maizeplant? Write ‘gram’ or ‘maize’ in theblank spaces in the figure aftermatching the roots with the figures.

In what way are the roots of gramand maize similar? In what way arethey different? There seem to be twodifferent types of roots, isn’t it? Arethere also other types of roots? Letus find out.

Activity 9

Go to an open ground where manyweeds are growing. Dig out a fewweeds, wash the soil off the roots andobserve them. Do you find that allthe weeds that you have dug out haveeither the kind of roots shown in Fig.7.17 (a) or as in Fig. 7.17 (b)?

For roots of the kind shown in

60 SCIENCE

Which colour did you use for theflower in Fig. 7.1? Are all flowerscolourful? Have you ever seenflowers on the plants of grass, wheat,maize, mango or guava? If you seeany flowers in these plants, are theybrightly coloured?

Let us study a few flowers closely.

Activity 10

We would require one bud and twofresh flowers each, of any of thefollowing– datura, china rose,mustard, brinjal, lady’s finger,gulmohur. Also a blade, a glass slideor a sheet of paper, a magnifyingglass and water.

Observe Fig. 7.20 carefully. Lookat the prominent parts of the openflower. These are the petals of theflower. Different flowers have petalsof different colours.Where do you think the petals arein a closed bud? Which is themost prominent part in a bud ?

Fig. 7.18. A stem as a two way street!

(b) (c)Fig 7.19 Rose: (a) A leafless branch (b) A branch with leaves (c) A branch with leaves and flowers Fig. 7.20 Bud and flower

Sepals

Petals

When choosing flowers to study,avoid using marigold, chrysanthe-mum or sunflower. You will learnin higher classes that they are notsingle flowers, but, groups offlowers.

(a)

and other parts of the plant. Theleaves prepare food. This food travelsthrough the stem and is stored indifferent parts of a plant. We eat someof these as roots— like carrot, radish,sweet potato, turnip and tapioca. Wealso eat many other parts of a plantwhere the food is stored.

Do you agree that stem is like atwo way street? Write down what goesup the stem and what comes down,in Fig. 7.18.

In the next section, we will studyabout the structure of a flower.

7.5 FLOWER

You are shown three branches of arose in Fig 7.19 (a), (b) and (c). Whichone will help you best to recognizethe plant?


Did you see that this part is madeof small leaf-like structures?They are called sepals. Take a flowerand observe its petals and sepals. Now,answer the following questions :

How many sepals does it have?Are they joined together?What are the colours of the petals

and the sepals?How many petals does your flower

have?Are they joined to one another or

are they separate?Do the flowers with joined sepals

have petals that are separate or arethey joined together?

Make a table based on theobservations of the whole class(Table 7.3). Add observations to thistable, from a field trip to a localitywhere there are plants with flowers.Fill the last two columns after youhave gone through the entiresection.

To see the inner parts of the flowerclearly, you have to cut it open, if itspetals are joined. For example, indatura and other bell shape flowers,the petals have to be cut lengthwiseand spread out so that the inner partscan be seen clearly (Fig. 7.21).

Table 7.3 Observations on flowers

foemaNrewolf

rebmuNruolocdna

slatepfo

rebmuNruolocdna

slapesfo

slapesehterArehtegotdenioj

?etarapesro

erasnematSroeerfyeht

?slatepotdenioj

litsiP/tneserP

tnesba

esoR ynaM)?ruoloC( )?ruoloC(5 etarapeS eerF tneserP

Remove the sepals and petals tosee the rest of the parts. Study theFig. 7.22 carefully, compare yourflower with the illustration and

Stamens Pistil

Anther

Filament

Fig. 7.21 A bell shaped flower

Fig. 7.22 Parts of a flower

Fig. 7.23 Parts of a stamen

62 SCIENCE

identify thestamens and pistilin your flower.

Look at Fig7.23 carefully. Itshows the differentkinds of stamenspresent in differentflowers. Can yourecognise both theparts of thestamens in yourflower? How many

stamens are there in your flower?Draw one stamen and label its parts.

The innermost part of a flower iscalled the pistil. If you cannot see itcompletely, remove the remainingstamens. Identify the parts of thepistil with the help of Fig. 7.24.

Draw a neat, labelled diagram ofthe pistil of your flower.

Activity 11

Let us now study the structure of theovary of a flower (Fig. 7.24). It is thelowermost and swollen part of thepistil. We will cut this part to studyhow it looks inside! Look at Fig. 7.25

(a) and (b) carefully to understandhow to cut the ovary of a flower.

Take two ovaries from differentflowers. Cut them in two differentways as shown in Fig. 7.25. Toprevent them from drying, put adrop of water on each of the twopieces of the ovary, you have cut.

Observe the inner parts of theovary using a lens (Fig. 7.26). Do yousee some small bead like structuresinside the ovary? They are calledovules. Draw and label the innerparts of the ovary in your notebook.

On your field trip, try to find outthe names of as many of the flowersas you can by asking the gardeneror any other person. Remember, notto pluck more flowers than you need.Based on what you have filled inTable 7.3, answer the followingquestions.

Do all flowers have sepals, petals,stamens and pistils? Are there flowersthat do not have any of these? Arethere flowers which have parts otherthan these?

Did you find any flowers whichhave sepals and petals that look

Fig. 7.24 Parts ofa pistil

StigmaStyle

Ovary

Fig. 7.25 Cutting an ovary (a) longitudinalcut and (b) transverse cut

(a) (b)

Ovules

Fig. 7.26 Inner structure of an ovary(a) longitudinal cut, (b) transversecut


srebmilC

tcudnoC

srepeerC

stoorsuorbiF

sbreH

animaL

stoorlaretaL

birdiM

eluvO

noitaneVlellaraP

lateP

eloiteP

sisehtnysotohP

litsiP

noitanevetaluciteR

lapeS

sburhS

nematS

toorpaT

noitaripsnarT

seerT

snieV

Plants are usually grouped into herbs, shrubs, trees, and climbers basedon their height, stems and branches.

The stem bears leaves, flowers and fruits.

A leaf usually has a petiole and a lamina.

The pattern of veins on the leaf is called venation. It can be reticulateor parallel.

Leaves give out water vapour through the process of transpiration.

Green leaves make their food by the process of photosynthesis usingcarbon dioxide and water in the presence of sunlight.

similar?Did you find any flowers in which

the number of sepals is different fromthe number of petals?

Do you now agree that thestructure of the flower is not alwaysthe same? The number of sepals,petals, stamens and pistils may also

be different in different flowers.Sometimes, some of these parts mayeven be absent!

We have studied some featuresand functions of leaves, stems androots. We studied the structure ofdifferent flowers. We will learn aboutthe function of flowers in higherclasses. We will also learn aboutfruits in higher classes.Key Words

Summary

64 SCIENCE

1. Correct the following statements and rewrite them in your notebook.

(a) Stem absorbs water and minerals from the soil.

(b) Leaves hold the plant upright.

(c) Roots conduct water to the leaves.

(d) The number of petals and sepals in a flower is always equal.

(e) If the sepals of a flower are joined together, its petals are also joinedtogether.

(f) If the petals of a flower are joined together, then the pistil is joined to thepetal.

2. Draw (a) a leaf, (b) a taproot and (c) a flower, you have studied for Table 7.3.

3. Can you find a plant in your house or in your neighborhood, which has a longbut a weak stem? Write its name. In which category would you classify it?

4. What is the function of a stem in a plant?

5. Which of the following leaves have reticulate venation?

Wheat, tulsi, maize, grass, coriander (dhania), China rose

6. If a plant has fibrous root, what type of venation do its leaves likely to have?

7. If a plant has leaves with reticulate venation, what kind of roots will it have?

8. Is it possible for you to recognize the leaves without seeing them? How?

9. Write the names of the parts of a flower.

10. Which of the following plants have you seen? of those that you have seen, whichone have flowers?

Grass, maize, wheat, chilli, tomato, tulsi, pipal, shisham, banyan, mango, jamun,guava, pomegranate, papaya, banana, lemon, sugarcane, potato, groundnut

11. Name the part of the plant which produces its food. Name this process.

12. In which part of a flower, you are likely to find the ovary?

13. Name two flowers, each with joined and separated sepals.

Roots absorb water and minerals from the soil and anchor the plant firmlyin the soil.

Roots are mainly of two types: tap root and fibrous roots.

Plants having leaves with reticulate venation have tap roots while plantshaving leaves with parallel venation have fibrous roots.

The stem conducts water from roots to the leaves (and other parts) andfood from leaves to other parts of the plant.

The parts of a flower are sepals, petals, stamens and pistil.

Exercises


SUGGESTED PROJECT AND ACTIVITIES1. BECOME A LEAF EXPERT

Do this activity with a number of leaves over a period of a few weeks. Forevery leaf that you wish to study, pluck it and wrap it in a wet cloth andtake it home. Now, put your leaf in a newspaper and place a heavy book onit. You can also put it under your mattress or a trunk! Take out the leafafter a week. Paste it on a paper and write a poem or story about it. Withyour leaf collection pasted in a book (a Herbarium), you can become quitean expert about leaves!

2. Names of plant parts are hidden in this grid. Search for them by going up,down, or even diagonally forward as well as backward. Have fun!

O V U L E L Y T S T E M

V E I N W Q H E R B P I

A N I M A L Z E X R N D

R F I L A M E N T M U R

Y A R A B L C O D B E I

L E E U O F O L G H I B

A L H I I R J A L K U R

T M T N O T P P Q R R A

E E N S T U F E H V W N

P Y A M G I T S Z Z N C

F L O W E R E H T N A H

S T A M E N N S E P A L

Body Movements8Sit absolutely still. Observe the

movements taking place inyour body. You must be

blinking your eyes, time to time.Observe the movements in your bodyas you breathe. There are so manymovements that happen in our body.

When you are writing in yournotebook which part of the body areyou moving? Or, when you turn andlook at your friend? Different partsof your body move while you remainat the same place, in these examples.You also move from one place toanother — you get up and go to yourteacher or to the school compound,or go home after school. You walk,run, skip, jump and move from placeto place.

Let us see how animals move fromplace to place by filling up Table 8.1,after discussing with our friends,teachers and parents.

Table 8.1 How do animals movefrom place to place?

laminA

desutrapydoBgnivomrofotecalpmorf

ecalp

seodwoHlaminaeht

?evom

woC sgeL klaW

snamuH

ekanS ydobelohW rehtilS

driB

tcesnI

hsiF

Walk, run, fly, jump, creep, crawl,slither and swim – these are only afew of the ways in which animalsmove from one place to another. Whyare there so many differences in theway that animals move from place toplace? Why is it that many animalswalk while a snake slithers or crawlsand a fish swims?

8.1 HUMAN BODY AND ITS MOVEMENTS

Let us look closely at some of ourown movements to begin with,before looking at all these varietiesof movements in animals.

Do you enjoy doing physicalexercise at school? How do youmove your hands and legs while

Boojho wonders aboutmovements in plants. Heknows they do not move fromplace to place, but, do theyshow any other kind ofmovements?

67BODY MOVEMENTS

doing different exercises? Let us trysome of the many movements, ourbody is capable of.

Bowl an imaginary ball at animaginary wicket. How did you moveyour arm? Did you rotate it at theshoulder in a circular movement?Did your shoulder also move? Liedown and rotate your leg at the hip.Bend your arm at the elbow and theleg at the knee. Stretch your armsideways. Bend your arm to touchyour shoulder with your fingers.Which part of your arm did youbend? Straighten your arm and tryto bend it downwards. Are you ableto do it?

Try to move the various partsof your body and record theirmovements in Table 8.2.

Why is it that we are able to movea few parts of our body easily invarious directions and some only inone direction? Why are we unable tomove some parts at all?

Activity 1

Place a scale length-wise on yourarm so that your elbow is in thecentre (Fig. 8.1).

Ask your friend to tie the scaleand your arm together.Now, try to bend yourelbow. Are you able to doit?

Fig. 8.1 Can you bendyour arm now?

Table 8.2 Movements in our body

setatoRyletelpmoc

setatoRsnrut/yltrap sdneB stfiL tonseoD

llataevom

kceN seY

tsirW

regniF

eenK

elknA

eoT

kcaB

daeH

woblE

mrA seY

Body

Part

Movement

68 SCIENCE

Did you notice that we are able tobend or rotate our body in placeswhere two parts of our body seem tobe joined together — like elbow,shoulder or neck? These places arecalled joints. Can you name moresuch joints? If our body has nojoints, do you think it would bepossible for us to move in any wayat all?

What exactly is joined together atthese joints?

Press your fingers against the topof your head, face, neck, nose, ear,back of the shoulder, hands and legsincluding the fingers and toes.

Do you get a feel of somethinghard pressing against your fingers?The hard structures are the bones.Repeat this activity on other parts ofyour body. So many bones!

Bones cannot be bent. So, howdo we bend our elbow? It is not onelong bone from the upper arm to ourwrist. It is different bones joinedtogether at the elbow. Similarly, thereare many bones present in each partof the body. We can bend or moveour body only at those points wherebones meet.

There are different types of jointsin our body to help us carry outdifferent movements and activities.Let us learn about some of them.

Ball and socket joints

Activity 2

Roll a strip of paper into a cylinder.Make a small hole in an old rubberor plastic ball (under supervision)

and push the paper cylinder into itas in Fig. 8.2. You can also stick thecylinder on the ball. Put the ball ina small bowl. Is the ball rotatingfreely inside the bowl? Is the papercylinder also rotating?

Now, imagine that the papercylinder is your arm and the ball isits end. The bowl is like the part ofthe shoulder to which your arm isjoined. The rounded end of one bonefits into the cavity (hollow space) ofthe other bone (Fig.8.3). Such a jointallows movements in all directions.Can you name another such jointyou can think of, recollecting thebody movements we tried at thebeginning of this section?

Fig. 8.2 Making a ball and socket joint

Fig. 8.3 A ball and socket joint

Pivotal JointThe joint where our neck joins thehead is a pivotal joint. It allows us to

69BODY MOVEMENTS

bend our head forward andbackward and turn the head to ourright or left. Try these movements.How are these movements differentfrom those of our arm that can rotatea complete circle in its ball andsocket joint? In a pivotal joint acylindrical bone rotates in a ring.

Hinge jointsOpen and close a door a few times.Observe the hinges of the doorcarefully. They allow the door to moveback and forth.

Activity 3Let us look at the kind of movementallowed by a hinge. Make a cylinderwith cardboard or thick chart paper,as shown in Fig. 8.4. Attach a smallpencil to the cylinder by piercing thecylinder at the centre, as shown.Make a hollow half cylinder fromcardboard such that the rolled upcylinder can fit inside it easily. Thehollow half cylinder with the rolledup cylinder sitting inside it, allowsmovement like a hinge. Try to movethe rolled up cylinder. How does itmove? How is this movementdifferent from what we saw with ourconstructed ball and socket joint? We

saw this kind of movement at theelbow in Activity 1. What we haveconstructed in Fig. 8.4 is differentfrom a hinge, of course. But, itillustrates the direction in which ahinge allows movement. The elbowhas a hinge joint that allows only aback and forth movement (Fig. 8.5).Can you think of more examples ofsuch joints?

Fixed jointsThere are some bones in our headthat are joined together at somejoints. The bones cannot move atthese joints. Such joints are calledfixed joints. When you open yourmouth wide, you can move yourlower jaw away from your head, isn’tit? Try to move your upper jaw, now.Are you able to move it? There is ajoint between the upper jaw and therest of the head which is a fixed joint.

We discussed only some of thejoints that connect parts of our body.

What gives the different parts ofthe body their different shapes?

If you wanted to make a doll, whatwill you make first? Perhaps aframework to give the doll shapebefore making its outer structure,

Fig. 8.5 Hinge joints of the knee

Fig. 8.4 Directions of movement allowed bya hinge like joint

70 SCIENCE

isn’t it? All the bones in our bodyalso form a framework to give ashape to our body. This frameworkis called the skeleton (Fig. 8.6.)

How do we know that this is theshape of a human skeleton? How dowe know the shapes of the differentbones in our body? We can havesome idea about the shape andnumber of bones in some parts ofour body by feeling them. One waywe could know this shape betterwould be to look at X-ray images ofthe human body.

Did you or anyone in your familyever have an X-ray of any part ofyour body taken? Sometimes whenwe are hurt, or have an accident,doctors use these X-ray images tofind out about any possible injuriesthat might have happened to thebones. The X-rays show the shapesof the bones in our bodies.

Feel the bones in your forearm,upper arm, lower leg and upper leg.Try to find the number of bones ineach part. Similarly, feel the bonesof your ankle and knee joints andcompare these with the X-ray images(Fig. 8.7).

Fig 8.7 X-ray images of ankle and kneejoints

Fig. 8.6 The Human skeleton Bend your fingers. Are you ableto bend them at every joint? Howmany bones does your middle fingerhave? Feel the back of your palm. Itseems to have many bones, isn’t it(Fig. 8.8)? Is your wrist flexible? It ismade up of several small bones. Whatwill happen if it has only one bone?

Activity 4

Take a deep breathe and hold it for alittle while. Feel your chest bones andthe back bone by gently pressing the

Fig. 8.8 Bones of the hand

71BODY MOVEMENTS

Make your friend stand with hishands pressed to a wall. Ask him toand try to push the wall. Do you seetwo bones standing where hisshoulders are? They are calledshoulder bones (Fig 8.11).

Observe Fig. 8.12 carefully. Thisstructure is made of pelvic bones.They enclose the portion of yourbody below the stomach. This is thepart you sit on.

The skull is made of many bonesjoined together (Fig. 8.13). It enclosesand protects a very important partof the body, the brain.

We discussed the many bones andthe joints of our skeleton. There are

middle of the chest and back at thesame time. Count as many ribs(bones of the chest) as possible.Observe Fig. 8.9 carefully andcompare with what you feel of thechest bones. We see that the ribs arecuriously bent. They join the chestbone and the backbone together toform a box. This is called the rib cage.Some important internal parts of ourbody lie protected inside this cage.

Ask a friend to touch his toes withoutbending his knees. Putyour fingers at thecentre of his back. Canyou feel some long andhard structure?Starting from theneck, move yourfingers downwards onthe back of your friend.What you feel is hisbackbone. It is madeof many small bones(Fig. 8.10). The ribcage is joined to thesebones.

If his backbonewere made up of onlyone long bone will yourfriend be able to bend?

Fig. 8.9 The rib cage

Fig. 8.10 Thebackbone

Fig. 8.11 Shoulder bones

Fig. 8.12 Pelvic bones.

Fig. 8.13 The skull

72 SCIENCE

some additional parts of the skeletonthat are not as hard as the bonesand which can be bent. These arecalled cartilage.

Feel your ear. Do you find anyhard bony parts that can be bent(Fig. 8.14)? There do not seem to beany bones here, isn’t it? Do younotice anything different between theear lobe and the portions above it(Fig. 8.15), as you press thembetween your fingers? You do feel

Do you see any change in your upperarm? Touch it with the other hand.Do you feel a swollen region insideyour upper arm? This is a muscle.The muscle bulged due tocontraction (it became smaller inlength). Now bring your arm back toits normal position. What happenedto the muscle? Is it still contracted?You can observe similar contractionof muscles in your leg when you walkor run.

When contracted, the musclebecomes shorter, stiffer and thicker.It pulls the bone.

Muscles work in pairs. When oneof them contracts, the bone is pulledin that direction. The other muscleof the pair relaxes. To move the bonein the opposite direction, the relaxedmusle contracts to pull the bonetowards its original postion, whilethe first relaxes. A muscle can onlypull. It cannot push. Thus, twomuscles have to work together tomove a bone (Fig. 8.16).

Are muscles and bones alwaysrequired for movement? How do otheranimals move? Do all animals have

Fig. 8.15 The earlobe

Fig. 8.14 Upper part ofear has cartilage

something in the upper parts of theear that is not as soft as the ear lobebut, not as hard as a bone, isn’t it?This is cartilage. Cartilage is alsofound in the joints of the body.

We have seen that our skeleton ismade up of many bones, joints andcartilage. You could see, bend andmove many of them. Draw a neatfigure of the skeleton in yournotebook.

We have learnt about the bones inour body and about joints that helpus move in different ways. What makesthe bones move the way they do? Letus find out.

Make a fist with one hand, bendyour arm at the elbow and touch yourshoulder with the thumb (Fig. 8.16).

Fig. 8.16 Two muscles work together tomove a bone

(a)

(b)

73BODY MOVEMENTS

and contractions, the earthworm canmove through soil. The body secretesa slimy substance to help themovement.

How does it fix parts of its bodyto the ground? Under its body, it hasa large number of tiny bristles (hairlike structures) projecting out. Thebristles are connected with muscles.The bristles help to get a good gripon the ground.

The earthworm, actually, eats itsway through the soil! Its body thenthrows away the undigested part ofthe material that it eats. This activityof an earthworm makes the soil moreuseful for plants.

Snail

Activity 6Collect a snail from a garden. Haveyou seen the rounded structure itcarries on its back (Fig. 8.18)?

Fig. 8.17 Movement of earthworm

bones? What about an earthworm ora snail? Let us study the manner ofmovement, that is, the gait of someanimals.

8.2 “GAIT OF ANIMALS”

Earthworm

Activity 5

Observe an earthworm moving onsoil in a garden. Gently lift it andplace it on a piece of blotting or filterpaper. Observe its movement (Fig.8.17). Then place it on a smoothglass plate or any slippery surface.Observe its movement now. Is itdifferent from that on paper? Do youfind that the earthworm is able tomove easily on a hard slipperysurface?

The body of an earthworm is madeup of many rings joined end to end.An earthworm does not have bones.

It has muscles which help to extendand shorten the body. Duringmovement, the earthworm firstextends the front part of the body,keeping the rear portion fixed to theground. Then it fixes the front endand releases the rear end. It thenshortens the body and pulls the rearend forward. This makes it moveforward by a small distance.Repeating such muscle expansions

Fig. 8.18 A snail

This is called the shell and it isthe outer skeleton of the snail, butis not made of bones. The shell is asingle unit and does not help inmoving from place to place. It has tobe dragged along.

Place the snail on a glass plateand watch it. When it starts moving,carefully lift the glass plate along withthe snail over your head. Observe itsmovements from beneath.

A thick structure and the head of

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the snail may come out of an openingin the shell. The thick structure isits foot, made of strong muscles.Now, carefully tilt the glass plate. Thewavy motion of the foot can be seen.Is the movement of a snail slow orfast as compared to an earthworm?

Cockroach

Activity 7

Observe a cockroach (Fig. 8.19).Cockroaches walk and climb as

well as fly in the air. They have threepairs of legs. These help in walking.The body is covered with a hard outerskeleton. This outer skeleton is made

hind limbs are typical for walking andperching. The bony parts of theforelimbs are modified as wings. Theshoulder bones are strong. Thebreastbones are modified to holdmuscles of flight which are used tomove the wings up and down(Fig. 8.20).

Fish

Activity 8

Make a paper boat. Put it in waterand push it with one narrow endpointing forward [Fig. 8.21 (a)]. Didit go into the water easily? Now holdthe boat sideways and push it intothe water from the broad side[Fig. 8.21 (b)]. Are you able to makethe boat move in water when youpush it from this side?

Fig. 8.19 A cockroach

of different units joined together andthat permits movement.

There are two pairs of wingsattached to the breast. Thecockroaches have distinct muscles —those near the legs move the legs forwalking. The breast muscles movethe wings when the cockroach flies.

BirdsBirds fly in the air and walk on theground. Some birds like ducks andswans also swim in water. The birdscan fly because their bodies are wellsuited for flying. Their bones arehollow and light. The bones of the

Fig. 8.20 Skeleton of a bird

(a)

(b)

Fig. 8.21 Playing with boats

75BODY MOVEMENTS

Have you noticed that the shapeof a boat is somewhat like a fish (Fig8.22)? The head and tail of the fishare smaller than the middle portionof the body – the body tapers at bothends. This body shape is calledstreamlined.

The shape is such that water canflow around it easily and allow thefish to move in water. The skeletonof the fish is covered with strongmuscles. During swimming, musclesmake the front part of the body curveto one side and the tail part swingstowards the opposite side. The fishforms a curve as shown in Fig. 8.23.Then, quickly, the body and tailcurve to the other side. This makesa jerk and pushes the body forward.A series of such jerks make the fishswim ahead. This is helped by thefins of the tail.

Fish also have other fins on theirbody which mainly help to keep thebalance of the body and to keepdirection, while swimming. Did youever notice that under water diverswear fin like flippers on their feet, tohelp them move easily in water?

How do snakes move?Have you seen a snake slither? Doesit move straight(Fig. 8.24)?

Snakes have a long backbone. Theyhave many thin muscles. They areconnected to each other even thoughthey are far from one another. Theyalso interconnect the backbone, ribsand skin.

The snake’s body curves intomany loops. Each loop of the snakegives it a forward push by pressingagainst the ground. Since its longbody makes many loops and eachloop gives it this push, the snakemoves forward very fast and not in astraightline.

We have learned about the use ofbones and muscles for themovements of different animals.Paheli and Boojho have manyquestions in their sacks about thedifferent movements in animals.So must you be having many

Fig. 8.22 Fish

Fig. 8.23 Movement in Fish Fig. 8.24 Movement in a snake

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enobkcaB

tniojtekcosdnallaB

seltsirB

egalitraC

ytivaC

tniojdexiF

slaminafotiaG

tniojegniH

elcsuM

noteleksretuO

senobcivleP

tniojlatoviP

egacbiR

senobredluohS

notelekS

denilmaertS

unanswered questions buzzing inyour minds? The ancient Greekphilosopher Aristotle, in his bookGait of Animals, asked himself thesequestions. Why do different animalshave the body parts that they dohave and how do these body partshelp animals to move the way theydo? What are the similarities anddifferences in these body partsbetween different animals? Howmany body parts are needed by

different animals for moving fromplace to place? Why two legs forhumans and four for cows andbuffaloes? Many animals seem tobe having an even number of legs,why? Why is the bending of our legsdifferent from that of our arms?

So many quest ions andperhaps we have looked for someanswers through our activities inthis chapter and we need to lookfor many more answers.

Key Words

77BODY MOVEMENTS

Bones and cartilage form the skeleton of the human body. It gives theframe and shape to the body and helps in movement. It protects theinner organs.

The skeleton comprises the skull, the back bone, ribs and the breastbone, shoulder and hipbones, and the bones of hands and legs.

The bones are moved by alternate contractions and relaxations of twosets of muscles.

The bone joints are of various kinds depending on the nature of jointsand direction of movement they allow.

Strong muscles and light bones work together to help the birds fly.They fly by flapping their wings.

Fish swim by forming loops alternately on two sides of the body.

Snakes slither on the ground by looping sideways. A large number ofbones and associated muscles push the body forward.

The body and legs of cockroaches have hard coverings forming an outerskeleton. The muscles of the breast connected with three pairs of legsand two pairs of wings help the cockroach to walk and fly.

Earthworms move by alternate extension and contraction of the bodyusing muscles. Tiny bristles on the underside of the body help in grip-ping the ground.

Snails move with the help of a muscular foot.


(a) Joints of the bones help in the ——————— of the body.

(b) A combination of bones and cartilages forms the _______ of the body.

(c) The bones at the elbow are joined by a ______________________ joint.

(d) The contraction of the _____________ pulls the bones during movement.

2. Indicate true (T) and false (F) among the following sentences.

(a) The movement and locomotion of all animals is exactly the same. ( )

(b) The cartilages are harder than bones. ( )

(c) The finger bones do not have joints. ( )

(d) The fore arm has two bones. ( )

(e) Cockroaches have an outer skeleton. ( )

Summary

Exercises

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3. Match the items in Column I with one or more items of Column II.

InmuloC IInmuloC

wajreppU ydobehtnosnifevah

hsiF noteleksretuonasah

sbiR riaehtniylfnac

lianS tniojelbavomminasi

hcaorkcoC traehehttcetorp

tnemevomwolsyrevswohs

ydobdenilmaertsaevah

4. Answer the following:

(a) What is a ball and socket joint?

(b) Which of the skull bones are movable?

(c) Why can our elbow not move backwards?


We discussed the many movements our bodies are capable of. Healthy bones,muscles, joints and cartilages are needed by the body for all these movements.Some of us suffer from conditions that could make these movements not so easy.In a whole class activity, try to find ways that one would manage everyday activi-ties, if any one of our body movements was not possible. In Activity 1, for in-stance, you tied a scale on your arm and disabled the elbow movement. Think ofother ways of restricting normal body movements and find ways that everydayactivities could then be managed.

The Living Organismsand Their Surroundings9

Paheli and Boojho went onvacation to many places ofinterest. One such trip took

them to the river Ganga in Rishik-esh. They climbed the mountains ofthe Himalayas, where it was verycold. They saw many kinds of treeson these mountains — oaks, pinesand deodars, very different from theones near their home on the plains!In yet another trip, they travelled toRajasthan and moved on camelsthrough the hot desert. Theycollected different kinds of cactusplants from this trip. Finally, theywent on a trip to Puri and visited thesea beach, dotted with casuarinatrees. While recollecting all the funthat they had on these trips, athought struck them. All these placeswere so different from one another,some were cold, some very hot anddry, and some places so humid. Andyet all of them had many organisms(living creatures) of various kinds.

They tried to think of a place onEarth where there may not be anyliving creatures. Boojho thought ofplaces near his home. Inside thehouse, he tried the cupboards. He hadthought that there may not be anyliving organisms here, but he foundone tiny spider in the cupboard.Outside the home too, there did notseem to be any place, he could thinkof, that did not have living creaturesof some kind or the other (Fig. 9.1).Paheli started thinking and reading

about far away places. She read thatpeople have even found tinyliving organisms in the openings ofvolcanoes!

9.1 ORGANISMS AND THE SURRO-UNDINGS WHERE THEY LIVE

Another thought that occurred toPaheli and Boojho was about thekinds of living organisms that werepresent in different locations thatthey had visited. The deserts hadcamels, the mountains had goatsand yak. Puri had some othercreatures — crabs on the beach andsuch a variety of fish being caughtby the fishermen at the sea! Andthen, there did seem to be somecreatures like ants that were presentin all these different locations. Thekinds of plants found in each ofthese regions were so different fromthe plants of the other regions. Whatabout the surroundings in these

Fig. 9.1 Search for living organisms

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different regions? Were they thesame?

Activity 1

Let us start with a forest. Think ofall the plants, animals and objectsthat can be found there. List themin Column 1 of Table 9.1. List things,animals and plants, found in theother regions that are also shown inthe table. You can collect theexamples scattered through thischapter to fill Table 9.1. Discuss alsowith your friends, parents andteachers, to find more examples tofill the tables. You can also consultmany interesting books in librariesthat talk of animals, plants andminerals of different regions.

Try and include many plants,animals and objects, big and small,in each of the columns in this table.What kind of objects will we find thatmay not be animals or plants?Perhaps parts of plants like driedleaves, or parts of animals, likebones. We may also find differentkinds of soils and pebbles. Water inthe oceans may have salts dissolvedin it as discussed in Chapter 5. Therecould be many more objects.

As we go through the chapter,keep adding more examples to Table9.1. We will discuss the table as wetravel through many more interestingplaces.

9.2 HABITAT AND ADAPTATION

What do you find from the plants andanimals listed in Activity 1? Did youfind a large variety in them? Look atwhat you have entered in the columnfor the desert and the column for thesea in Table 9.1. Did you list verydifferent kind of organisms in thesetwo columns?

What are the surroundings like,in these two regions?

In the sea, plants and animals aresurrounded by saline (salty) water.Most of them use the air dissolvedin water.

There is very little water availablein the desert. It is very hot in theday time and very cold at night inthe desert. The animals and plantsof the desert live on the desertsoil and breathe air from thesurroundings.

The sea and the desert are verydifferent surroundings and we findvery different kind of plants andanimals in these two regions, isn’t it?

Table 9.1 Animals, plants and other objects found indifferent surroundings

tserofehtnI sniatnuomnO tresedehtnI aesehtnI ?rehtoynA

81THE LIVING ORGANISMS AND THEIR SURROUNDINGS

Let us look at two very different kindsof organisms from the desert and thesea – a camel and a fish. The bodystructure of a camel helps it tosurvive in desert conditions. Camelshave long legs which help to keeptheir bodies away from the heat ofthe sand (Fig. 9.2). They excretesmall amount of urine, their dung isdry and they do not sweat. Sincecamels lose very little water from theirbodies, they can live for many dayswithout water.

Let us look at different kinds offish. Some of these are shown inFig. 9.3. There are so many kinds offish, but, do you see that they allhave something common about theirshape? All the ones shown here havethe streamlined shape that wasdiscussed in Chapter 8. This shapehelps them move inside water. Fishhave slippery scales on their bodies.These scales protect the fish and alsohelp in easy movement throughwater. We discussed in Chapter 8,that fish have flat fins and tails thathelp them to change directions andkeep their body balance in water.Gills present in the fish help themto use oxygen dissolved in water.

We see that the features of a fishhelp it to live inside water and thefeatures of a camel help it to survivein a desert.

We have taken only two examplesfrom a very wide variety of animalsand plants that live on the Earth. Inall this variety of organisms, we willfind that they have certain featuresthat help them live in the surround-ings in which they are normallyfound. The presence of specificfeatures or certain habits, whichenable a plant or an animal to livein its surroundings, is calledadaptation. Different animals areadapted to their surroundings indifferent ways.

The surroundings where organ-isms live is called a habitat. Theorganisms depend for their food,water, air, shelter and other needson their habitat. Habitat means adwelling place (a home). Severalkinds of plants and animals mayshare the same habitat.

The plants and animals that liveon land are said to live in terrestrialhabitats. Some examples of terrest-rial habitats are forests, grasslands,deserts, coastal and mountainregions. On the other hand, thehabitats of plants and animals that

Fig. 9.2 Camels in their surroundings Fig. 9.3 Different kinds of fish

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live in water are called aquatichabitats. Ponds, swamps,lakes, rivers and oceans are someexamples of aquatic habitats. Thereare large variations in forests,grasslands, deserts, coastal andmountain regions located in differentparts of the world. This is true for allaquatic habitats as well.

The living things such as plantsand animals, in a habitat, are itsbiotic components. Various non-living things such as rocks, soil, airand water in the habitat constituteits abiotic components. Sunlightand heat also form abioti ccompon-ents of the habitat.

We know that some plants growfrom seeds. Let us look at someabiotic factors and their effect onseeds as they grow into youngplants.

Activity 2Recall Activity 5 in Chapter 1 — wemade sprouts from moong and chanaseeds. When the seed turned into asprout, it germinated. This was thebeginning of a new plant, from theseed.

Collect some dry moong seeds.Keep a small heap of seeds aside andsoak the rest in water for a day.Divide the soaked seeds into fourparts. Keep one part completelysubmerged in water for 3-4 days. Donot disturb the dry seeds and thosesubmerged in water. Keep one partof soaked seeds in a sunny room andanother in a completely darkregion like a cupboard that does notallow any light to come in. Keep thelast part in very cold surroundings,say, in a refrigerator or with icearound them. Set these three partsto germinate by rinsing them anddraining the water every day. Whatdo you notice, after a few days? Dothe seeds in all the five partsgerminate equally? Do you findslower or no germination in anyof these?

Do you find that abiotic factorslike air, water, light and heat are veryimportant for growth of plants. Infact, these abiotic factors areimportant for all living organisms.

We find that organisms exist invery cold as well as very hot climatesand surroundings, isn’t it? How do

There are some changes that can happen in an organism over a shortperiod of time to help them adjust to some changes in their surroundings.For instance, if we live in the plains and suddenly go to high mountainregions, we may experience difficulty in breathing and doing physicalexercise for some days. We need to breathe faster when we are on highmountains. After some days, our body adjusts to the changed conditionson the high mountain. Such small changes that take place in the body ofa single organism over short periods, to overcome small problems due tochanges in the surroundings, are called acclimatisation. These changesare different from the adaptations that take place over thousands of years.


they manage to survive? That iswhere, adaptation comes in.

Adaptation does not take place ina short time. Over thousands ofyears, the abiotic factors of a regionchange. Those animals which cannotadapt to these changes die out, andonly the adapted ones survive.Animals adapt to different abioticfactors in different ways. The resultis variety of organisms present indifferent habitats.

Let us look at some habitats, theabiotic factors of these, and theadaptations of animals to thesehabitats.

9.3 A JOURNEY THROUGH

DIFFERENT HABITATS

Some Terrestrial HabitatsDesertsWe discussed the abiotic factors ofa desert and the adaptations incamels to these. What about otheranimals and plants that are foundin deserts? Do they have the samekind of adaptations?

There are desert animals like ratsand snakes, which do not have thelong legs that the camel has. To stayaway from the intense heat duringthe day, they stay in burrows deepin the sand (Fig 9.4). These animalscome out only during the night,when it is cooler.

Fig. 9.5 shows some typical plantsthat grow in a desert. How are theseadapted to the desert?

Activity 3

Bring a potted cactus and a leafyplant to the classroom. Tie polythene

bags to some parts of the two plants,as was done for Activity 4 in Chapter7, where we studied transpiration inplants. Leave the potted plants in thesun and observe after a few hours.What do you see? Do you notice anydifference in the amount of watercollected on the two polythene bags?

Desert plants lose very little waterthrough transpiration. The leaves indesert plants are either absent, verysmall, or they are present in theshape of spines. This helps inreducing loss of water from the leavesthrough transpiration. The leaf-likestructure you see in a cactus is, infact, its stem (Fig. 9.5). Photo-synthesis in these plants is usuallycarried out by the stems. The stemis also covered with a thick waxylayer, which helps to retain water.

Fig. 9.5 Some typical plants that grow indesert

Fig. 9.4 Desert animals in burrows

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Most desert plants have roots thatgo very deep into the soil forabsorbing water.

Mountain regionsThese habitats are normally very coldand windy. In some areas, snowfallmay take place in winters.

There is a large variety of plantsand animals living in the mountainregions. Have you seen the kind oftrees shown in Fig. 9.6?

Animals living in the mountainregions are also adapted to theconditions there (Fig. 9.7). They havethick skin or fur to protect them fromcold. For example, yaks have long hairto keep them warm. Snow leopard hasthick fur on its body including feet

Fig. 9.6 Trees of a mountain habitat

If you live in a mountain regionor have visited one, you may haveseen a large number of such trees.But, have you ever noticed such treesnaturally growing in other regions?

How are these trees adapted to theconditions prevailing in theirhabitat? These trees are normallycone shaped and have slopingbranches. The leaves of some of thesetrees are needle-like. This helps therainwater and snow to slide off easily.There could be trees with shapes verydifferent from these that are alsopresent on mountains. They mayhave different kind of adaptations tosurvive on the mountains.

Fig. 9.7 (a)Snow leopards,(b) yak and (c)mountain goatsare adapted to

mountainhabitats

(b)

(c)

(a)


and toes. This protects its feet fromthe cold when it walks on the snow.The mountain goat has strong hoovesfor running up the rocky slopes of themountains.

As we go up in the mountainousregions, the surroundings changeand we see different kinds ofadaptations at different heights.

GrasslandsA lion lives in a forest or a grasslandand is a strong animal that can huntand kill animals like deer. It is lightbrown in colour. Look at the pictureof a lion and that of a deer (Fig. 9.8).How are the eyes placed in the facefor these two animals? Are they inthe front or on the side of the face?Lions have long claws in their frontlegs that can be withdrawn insidethe toes. Do the features of a lion

Fig. 9.8 (a) Lion and (b) deer

(a)

(b)

help it in any way to survive? It’s lightbrown colour helps it to hide in drygrasslands when it hunts for prey(animals to eat). The eyes in front ofthe face allow it to have a correct ideaabout the location of its prey.

A deer is another animal that livesin forests and grasslands. It hasstrong teeth for chewing hard plantstems of the forest. A deer needs toknow about the presence of predators( animals like lion that make it theirprey ) in order to run away from themand not become their prey. It haslong ears to hear movements ofpredators. The eyes on the side of itshead allow it to look in all directionsfor danger. The speed of the deerhelps them to run away from thepredators.

There are many other features ofa lion, a deer or other animals andplants that help them to survive intheir habitat.

Some Aquatic HabitatsOceansWe already discussed how fish areadapted to live in the sea. Many othersea animals have streamlined bodiesto help them move easily in water.There are some sea animals likesquids and octopus, which do nothave this streamlined shape. Theystay deeper in the ocean, near theseabed and catch any prey thatmoves towards them. However, whenthey move in water they make theirbody shapes streamlined. Theseanimals have gills to help them useoxygen dissolved in water.

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There are some sea animals likedolphins and whales that do nothave gills. They breathe in airthrough nostrils or blowholes thatare located on the upper parts of theirheads. This allows them to breathein air when they swim near thesurface of water. They can stay insidethe water for a long time withoutbreathing. They come out to thesurface from time to time, to breathein air. Did you ever see thisinteresting activity of dolphins intelevision programme or films onocean life?

Ponds and lakesHave you seen plants growing inponds, lakes, rivers and even somedrains? Go on a field trip to a nearbypond, if possible, and try to draw thekinds of plants that are seen there.How are the leaves, stems and roots ofthese plants placed?

Some of these plants have theirroots fixed in the soil below the water(Fig. 9.9). In terrestrial plants, rootsnormally play a very important role inthe absorption of nutrients and waterfrom the soil. However, in aquaticplants, roots are much reduced in sizeand their main function is to hold theplant in place.

The stems of these plants arelong, hollow and light. The stemsgrow up to the surface of water whilethe leaves and flowers, float on thesurface of the water.

Some aquatic plants are totallysubmerged in water. All parts of suchplants grow under water. Some ofthese plants have narrow and thinribbon-like leaves. These can bendin the flowing water. In somesubmerged plants, leaves are oftenhighly divided, through which thewater can easily flow withoutdamaging them.

Frogs usually have ponds as theirhabitat. Frogs can stay both insidethe pond water as well as move onland. They have strong back legs thathelp them in leaping and catchingtheir prey. They have webbed feetwhich help them swim in water.

We have discussed only a fewcommon animals and plantscompared to the wide variety that livein the different habitats. You may havealso noticed the very wide variety inplants around you, when youprepared a herbarium as part of thesuggested activities in Chapter 7.Imagine the kind of variety that youcould see in a herbarium of leaves ofplants from all regions of the Earth!

Fig. 9.9 Some aquatic plants float on water.Some have their roots fixed in the soil at thebottom. Some aquatic plants are compltely

submerged in water.


9.4 LIVING THINGS AROUND US

We went on a journey throughdifferent habitats and discussedmany plants and animals. InActivity 1, we listed objects, plantsand animals found in differentsurroundings. Suppose we stop awhile and think which examples inour list are living? Let us think ofexamples from a forest. Trees,creepers, small and big animals,birds, snakes, insects, rocks, soil,water, air, dry leaves, dead animals,mushrooms and moss may be onlysome of the objects that are presentin the forest. Which of these areliving?

Think of objects that you can seearound you at this moment andgroup them as living and non-living.In some cases, it is easy for us toknow. For example, objects like chairor a table in our homes we know thatthey are not alive. Paheli was readingthis rhyme from Complete Nonsensewritten by Edward Lear:

Paheli and Boojho found thepoem so very funny, because theyknew that a chair or a table is notalive and it cannot talk, walk orsuffer from the usual problems thatall of us face.

A chair, table, stone or a coin. Weknow that they are not alive.Similarly, we do know that we arealive and so are all the people of theworld. We also see animals aroundus that are so full of life — dogs, cats,monkeys, squirrels, insects andmany others.

How do we know that somethingis living? Often, it is not so easy todecide. We are told that plants areliving things, but they do not appearto move like a dog or a pigeon. Onthe other hand, a car or a bus canmove, still we consider them as non-living. Plants and animals appear togrow in size with time. But then, attimes, clouds in the sky also seem togrow in size. Does it mean thatclouds are living? No! So, how doesone distinguish between living andnon-living things? Do living thingshave some common characteristicsthat make them very different fromthe non-living?

You are a wonderful example of aliving being. What characteristics doyou have which make you differentfrom a non-living thing? List a few ofthese characteristics in yournotebook. Look at your list and markthose characteristics that you havelisted, which may also be found inanimals or plants.

Some of these characteristics areperhaps common to all living things.

Said the Table to the Chair,

’You can hardly be aware,

’How I suffer from the heat,

’And from chilblains on my feet!

’If we took a little walk,

’We might have a little talk!

’Pray let us take the air!’

Said the Table to the Chair.

Said the Chair to the table,

’Now you know we are not able!

’How foolishly you talk,

’When you know we cannot walk!’

Said the Table with a sigh,

’It can do no harm to try,

’I’ve as many legs as you,

’Why can’t we walk on two?’

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Do all living things needfood?

In Chapters 1 and 2, we learnt thatall living things need food and howessential it is to animals and to us.We have also learnt that plants maketheir own food through the processof photosynthesis. Animals dependon plants and other animals for theirfood.

Food gives organisms the energyneeded for them to grow. Organismsalso need this energy for other lifeprocesses that go on inside them.

Do all living things showgrowth?Does the kurta you had four yearsback, still fit you? You cannot wear itany more, isn’t it? You must havegrown taller during these years. Youmay not realise it, but you are growingall the time and in few more yearsyou will become an adult. (Fig 9.10).

Young ones ofanimals also growinto adults. Youwould surely havenoticed pups of adog grow intoadults. A chicknhatched from anegg, grows into ahen or a cock.(Fig 9.11).

Plants alsogrow. Look around you and see a fewplants of a particular type. Some arevery small and young, some aregrown. They may all be in differentstages of growth. Look at the plantsafter a few days and weeks. You mayfind that some of them have grownin size. Growth seems to be commonto all living things.

Do you think, non-living thingscannot show growth?

Do all living things respire?Can we live without breathing? Whenwe inhale, the air moves from outsideto the inside of the body. When webreathe out, the air moves frominside our body to outside. Breathingis part of a process called respiration.In respiration, some of the oxygen ofthe air we breathe in, is used by theliving body. We breathe out thecarbon dioxide produced in thisprocess.

The process of breathing inanimals like cows, buffaloes, dogs orcats is similar to humans. Observeany one of these animals while theyare taking rest, and notice themovement of their abdomen. Thisslow movement indicates that theyare breathing.Fig. 9.10 A baby grows into an adult

Fig. 9.11 A chickengrows into an adult


Respiration is necessary for allliving organisms. It is throughrespiration that the body finallyobtains energy from the food it takes.

Some animals may have differentmechanisms for the exchange ofgases, which is a part of therespiration process. For example,earthworms breathe through theirskin. Fish, we have learnt, have gillsfor using oxygen dissolved in water.The gills absorb oxygen from the airdissolved in water.

Do plants also respire? Exchangeof gases in plants mainly takes placethrough their leaves. The leaves takein air through tiny pores in them anduse the oxygen. They give out carbondioxide to the air.

We learnt that in sunlight, plantsuse carbon dioxide of air to producetheir own food and give out oxygen.Plants produce their food only duringthe daytime whereas respiration inthem takes place day and night. Theamount of oxygen released in theprocess of food preparation by plantsis much more than the oxygen theyuse in respiration.

Do all living things respondto stimuli?How do you respond, if you suddenlystep on a sharp object like a thorn,while walking barefoot? How do youfeel when you see or think aboutyour favourite food? You suddenlymove from a dark place into brightsunlight. What happens? Your eyesshut themselves automatically for amoment till they adjust to thechanged bright surroundings. Yourfavourite food, bright light and a

thorn, in the above situations aresome examples of changes in yoursurroundings. All of us respondimmediately to such changes.Changes in our surroundings thatmakes us respond to them, are calledstimuli.

Do other animals also respond tostimuli? Observe the behaviour ofanimals, when the food is served tothem. Do you find them suddenlybecoming active on seeing the food?When you move towards a bird, whatdoes it do? Wild animals run awaywhen bright light is flashed towardsthem. Similarly, cockroaches beginto move to their hiding places if thelight in the kitchen is switched onat night. Can you give some moreexamples of responses of animals tostimuli?

Do plants also respond to stimuli?Flowers of some plants bloom onlyat night. In some plants flowers closeafter sunset. In some plants likemimosa, commonly known as‘touch-me-not’, leaves close or foldwhen someone touches them. Theseare some examples of responses ofplants towards changes in theirsurroundings.

Activity 4Place a potted plant in a room a littleaway from a window through whichsunlight enters some time during theday (Fig. 9.12). Continue wateringthe plant for a few days. Does theplant grow upright, like plants outin the open? Note the direction inwhich it bends, if it is not growingupright. Do you think, this may bein response to some stimulus?

90 SCIENCE

All living things respond tochanges around them.

Living organisms and excre-tionAll living things take food. Not allthe food that is eaten is really used,only a part of it is utilised by thebody. What happens to the rest?This has to be removed by the bodyas wastes. Our body also producessome wastes in other life processes.The process of getting rid of thesewastes by the living organisms isknown as excretion.

Do plants also excrete? Yes, theydo. However, the mechanisms in plantsare a little different. Some harmful orpoisonous materials do get producedin plants as wastes. Some plants findit possible to store the waste productswithin their parts in a way that theydo not harm the plant as a whole.Some plants remove waste productsas secretions.

Excretion is another chara-cteristics common to all living things.

Do all livingthingsreproducetheir ownkind?Have you ever seennests of some birdslike pigeons? Many

birds lay their eggs in the nest. Someof the eggs may hatch and youngbirds come out of these (Fig. 9.13).

Animals reproduce their ownkind. The mode of reproduction maybe different, in different animals.Some animals produce theiryoung ones through eggs. Someanimals give birth to the young ones(Fig. 9.14).

Plants also reproduce. Likeanimals, plants also differ in theirmode of reproduction. Many plants

Fig. 9.12 Plant respond to light

(a) (b)

Fig. 9.13 A Birds lay eggs whichafter hatching produce (b) young ones

Fig. 9.14 Some animals which give birth totheir young ones


reproduce through seeds. Plantsproduce seeds, which can germinateand grow into new plants (Fig.9.15).

Some plants also reproducethrough parts other than seeds. Forexample, a part of a potato with abud, grows into a new plant(Fig 9.16).

to a gardner, if possible, on the careto be given to cuttings to make themgrow into plants.

Living things produce moreof their own kind throughrepro-duction. It takes place inmany different ways, for differentorganisms.

Do all living things move?In Chapter 8, we discussed thevarious ways in which animals move.They move from one place to anotherand also show other bodymovements.

What about plants? Do they alsomove? Plants are generally anchoredin soil so they do not move from oneplace to another. However, varioussubstances like water, minerals andthe food synthesised by them movesfrom one part of the plant to other.Have you noticed any other kind ofmovement in plants? Opening orclosing of flowers? Do you recall howsome plants show movement inresponse to certain stimuli?

We also have some non-livingthings moving, of course. A bus,car, a small piece of paper, cloudsand so on. Is there somethingdifferent in these movements fromthe movements of living beings?

There is such a variety of livingorganisms, but, all of them showsome common characteristics, as wehave discussed. Yet another commoncharacteristic is that living beingsdie. Because organisms die,organism types can survive overthousands of years only if theyreproduce their own kind. Onesingle organism may die without ever

Fig. 9.15 A seed from a plant germinatesinto a new plant

Fig. 9.16 A new plant grows from a bud ofpotato

Plants also reproduce throughcuttings. Would you like to grow aplant in this way yourself?

Activity 5Take a cutting from a rose or amenhdi plant. Fix it in the soil andwater it regularly. What do youobserve, after a few days?

It may not be easy to grow plantsfrom cuttings. Do not be disappointedif your cutting does not grow. Talk

92 SCIENCE

reproducing, but, the type oforganism can exist only if there isreproduction.

We see that, all living things seemto have some common chara-cteristics. They all need food, respire,respond to stimuli, reproduce, showmovement, grow and die.

Do we find some non-living thingsthat also show some of thesecharacteristics? Cars, bicycle, clocksand the water in the river move. Themoon moves in the sky. A cloudgrows in size right in front of oureyes. Can such things be calledliving? We ask ourselves, do theseobjects also show all the othercharacteristics of living things?

In general, something that isliving may have all the characteristicsthat we have discussed, while non-living things may not show all thesecharacteristics at the same time.

Is this always true? Do we alwaysfind that living things definitely showall the characteristics of the living thatwe have discussed? Do we always findthat non-living things may show onlysome of these characteristics andnever all of them?

To understand this a little better,let us look at a specific example.

Consider any seed, say, moong. Is itliving? It can stay in a shop formonths and not show any growth orsome of the other characteristics oflife. However, we bring the same seedand plant it in soil, water it and itturns into a whole plant. Did theseed — need food, did it excrete, growor reproduce when it was in the shopfor many months?

We see that there can be cases whenwe cannot easily say that a thing hasall the characteristics that we havediscussed, for it to be called living.

“What then is life?”Push your hand deep inside a sackof wheat. Do you find it is warminside? There is some heat beingproduced inside the sack of wheat.The seeds respire and in that processgive out some heat.

We see that respiration is a processthat takes place in seeds even whensome of the other life processes maynot be very active.

It may not be very easy to answerour question — “what then is life”?However, looking at all the diversityof living beings around us, we canconclude that “life is beautiful”!

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Key Words


The surroundings where plants and animals live, is called their habitat.

Several kinds of plants and animals may share the same habitat.

The presence of specific features and habits, which enable a plant or ananimal to live in a particular habitat, is called adaptation.

There are many types of habitats, however, these may be broadly groupedas terrestrial (on the land) and aquatic (in water).

There is a wide variety of organisms present in different habitats.

Plants, animals and microorganisms together constitute biotic compo-nents.

Rocks, soil, air, water, light and temperature are some of the abioticcomponents of our surroundings.

Living things have certain common characteristics — they need food,they respire and, excrete, respond to their environment, reproduce, growand show movement.

1. What is a habitat?

2. How are cactus adapted to survive in a desert?

3. Fill up the blanks

(a) The presence of specific features, which enable a plant or an animal to livein a particular habitat, is called .

(b) The habitats of the plants and animals that live on land are called habitat.

(c) The habitats of plants and animals that live in water are called habitat.

(d) Soil, water and air are the ———— factors of a habitat.

(e) Changes in our surroundings that make us respond to them, arecalled .

4. Which of the things in the following list are nonliving?

Plough, Mushroom, Sewing machine, Radio, Boat, Water hyacinth, Earthworm

5. Give an example of a non-living thing, which shows any two characteristics ofliving things.

6. Which of the non-living things listed below, were once part of a living thing?

Butter, Leather, Soil, Wool, Electric bulb, Cooking oil, Salt, Apple, Rubber

7. List the common characteristics of the living things.

8. Explain, why speed is important for survival in the grasslands for animalsthat live there. (Hint: There are few trees or places for animals to hide ingrasslands habitats.)

Summary

Exercises

94 SCIENCE


1. Many magazines and newspapers talk about possibility of life outside theEarth. Read these articles and have a discussion in the class about whatcould be defined as life outside Earth.

2. Visit a local zoo and find out what special arrangements are made for theanimals that have been brought there from different habitats.

3. Find out where are the habitats of the polar bear and the penguin. For eachanimal, explain two ways in which it is well adapted to its habitat.

4. Find out which animals live in the foot-hills of the Himalayas. Find out if thetypes and varieties of animals and plants changes as one goes higher intothe mountain regions of the Himalayas.

5. Make a habitat album. Try to obtain pictures of animals and plants that youhave listed in Activity 1 and paste these under different habitat sections inthe album. Draw the leaf shapes and structures for trees found in thesedifferent regions and include these in the album. In addition, draw the pat-terns of branching found in trees of these different regions and include thesealso in the album.

What isits

nameand

habitat

10Motion and Measurementof Distances

here was a general discussion among the children inPaheli and Boojho's class

about the places they had visitedduring the summer vacations.Someone had gone to their nativevillage by a train, then a bus, andfinally a bullock cart. One studenthad travelled by an aeroplane. An-other spent many days of his holi-days going on fishing trips in hisuncle's boat.

The teacher then asked them toread newspaper articles that men-tioned about small wheeled vehiclesthat moved on the soil of Mars andconducted experiments. Thesevehicles were taken by spacecraft allthe way to Mars!

Meanwhile, Paheli had beenreading stories about ancient Indiaand wanted to know how peopletravelled from one place to anotherin earlier times.

10.1 STORY OF TRANSPORT

Long ago people did not have anymeans of transport. They used tomove only on foot and carry goodseither on their back or usinganimals.

For transport along water routes,boats were used from ancient times.To begin with, boats were simplelogs of wood in which a hollow cavitycould be made. Later, people learnt Fig 10.1 Means of transportation

T to put together different pieces ofwood and give shapes to the boats.These shapes imitated the shapes ofthe animals living in water. Recallour discussions of this streamlinedshape of fish in Chapters 8 and 9.

Invention of the wheel made agreat change in modes of transport.The design of the wheel wasimproved over thousands of years.Animals were used to pull vehiclesthat moved on wheels.

Until the beginning of the 19thcentury, people still depended onanimal power to transport themfrom place to place. The inventionof steam engine introduced a newsource of power. Railroads weremade for steam engine driven

96 SCIENCE

carriages and wagons. Later cameautomobiles. Motorised boats andships were used as means oftransport on water. The early years of1900 saw the developmentof aeroplanes. These were laterimproved to carry passengers andgoods. Electric trains, monorail,supersonic aeroplanes and spacecraftare some of the 20th centurycontributions.

Fig. 10.1 shows some of the dif-ferent modes of transport. Placethem in the correct order — fromthe earliest modes of transport to themost recent.

Are there any of the early modesof transport that are not in usetoday?

10.2 HOW FAR HAVE YOUTRAVELLED? HOW WIDE ISTHIS DESK?

How did people know how far theyhave travelled?

How will you know whether youcan walk all the way to your schoolor whether you will need to take a busor a rickshaw to reach your school?When you need to purchasesomething, is it possible for you towalk to the market? How will youknow the answers to these questions?

It is often important to know howfar a place is, so that we can havean idea how we are going to reachthat place — walk, take a bus or atrain, a ship, an aeroplane or evena spacecraft!

Sometimes, there are objectswhose length or width we need toknow.

In Paheli and Boojho's class-room, there are large desks whichare to be shared by two students.Paheli and Boojho share one desk,but, frequently end up fighting thatthe other is using a larger share ofthe desk.

On the teacher's suggestion, theydecided to measure the length of thedesk, make a mark exactly in themiddle of it and draw a line toseparate the two halves of the desk.

Both of them are very fond ofplaying gilli danda with their friends.Boojho brought a set of gilli anddanda with him.

Here is how they tried to measurethe length of the desk using thedanda and the gilli (Fig. 10.2).

The desk seems to be having alength equal to two danda lengthsand two lengths of the gil l i.Drawing a line in the middle of thedesk leaves each of them happywith a half of the desk equal to adanda and a gilli in length. After afew days, the marked line getswiped out. Boojho now has a newset of gilli and danda as he lost hisold one. Here is how, the length ofthe desk seems to be measuringusing the gill i and danda(Fig. 10.3).

Hello! Now, when measured with

Fig. 10.3 Measuring the length of the desk

with a different set of gilli and danda

Fig. 10.2 Measuring the length of a deskwith gilli and danda

97MOTION AND MEASUREMENT OF DISTANCES

the new set of gilli and danda, thedesk length seems to be about twodanda lengths, one gilli length witha small length still left out. This isless than one gilli length. Now what?

What would you suggest Paheliand Boojho do, to measure thelength of the whole desk? Can theyuse a cricket wicket and bails tomeasure the length or do you thinkthat this might create the similarproblem?

One thing they could do is to takea small length of string and mark twopoints on it. This will be a stringlength. They can measure the widthof the desk in string lengths (Fig.10.4). How can they use the string tomeasure distances less than thelength of a string? They can fold thestring and mark it into

12

, 14

and 18

'string lengths'. Now, perhaps Paheliand Boojho can measure the exactlength of the desk using the string.

You would say that they shoulduse the scale in their geometry boxand solve their problem? Yes, Ofcourse!

Boojho has been reading aboutthe way people used to measure

distances before such standardscales were made and he has beentrying to follow different methods ofmeasuring distances.

There are so many occasions whenwe come across a need to measurelengths and distances. The tailorneeds to measure the length of thecloth to know if it is enough to stitcha kurta. A carpenter needs tomeasure the height and width of acupboard to know how much woodhe would need to make its door. Thefarmer needs to know the length andbreadth or the area of his land to knowhow much seed he can sow and howmuch water would be needed for hiscrops.

Suppose, you are asked how tallyou are? You want to tell the lengthof a straight line from the top of yourhead to the heel of your feet.

How long is this broom?How wide is this desk?How far is it from Delhi to

Lucknow?How far away is the Moon from

the Earth?All these questions have one

thing in common. They all concerndistance between two places. Thetwo places may be close enough, likethe two ends of a table or they maybe far apart, like Jammu andKanyakumari.

Let us do a few measurementsto see what exactly we need to do,when we measure distances orlengths.

10.3 SOME MEASUREMENTS

Activity 1Work in groups and each of you dothis activity one by one. Using yourfoot as a unit of length, measure the

Fig. 10.4 Measuring the length of the desk

with string lengths

98 SCIENCE

length and breadth of the classroom.It is possible that while measuringthese you may find some partremains to be measured as it issmaller than your foot. Use a stringto measure the length of a part ofyour foot as you did before. Recordyour observations in Table 10.1.

Table 10.1 Measuring length andbreadth of classroom

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Activity 2

Work in a group and each of you useyour handspan as a unit to measurethe width of a table or a desk in theclassroom (Fig. 10.5).

quantity. This known fixed quantityis called a unit. The result of ameasurement is expressed in twoparts. One part is a number. Theother part is the unit of themeasurement. For example, if inActivity 1, the length of the room isfound to be 12 lengths of your foot,then 12 is the number and 'footlength' is the unit selected for themeasurement.

Now, study all the measurementsrecorded in Table 10.1 and 10.2. Areall the measurements for the roomusing everybody's foot, equal? Areeverybody's measurement, byhandspan, of the width of the tableequal? Perhaps the results could bedifferent as the length of yourhandspan and that of your friendsmay not be the same. Similarly, thelength of the foot may be slightlydif ferent for all the students.Therefore, when you tell yourmeasurement using your handspanor length of foot as a unit to others,they will not be able to understandhow big the actual length is, unlessthey know the length of yourhandspan or foot.

We see therefore, that somestandard units of measurement areneeded, that do not change fromperson to person.

Fig. 10.5 Measuring the width of a table

with a handspan

Here too, you may find that youneed string lengths equal to yourhandspan and then fractions ofthis string length to make the mea-surement. Record all observationsin Table 10.2.

We see that, measurementmeans the comparison of anunknown quantity with some known

Table 10.2 Measuring width of a

table

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10.4 STANDARD UNITS OF

MEASUREMENTS

In ancient times, the length of a foot,the width of a finger, and the dis-tance of a step were commonly usedas different units of measurements.

The people of the Indus valleycivilisation must have used verygood measurements of lengthbecause we see evidence inexcavations of perfectly geometricalconstructions.

A cubit as the length from theelbow to the finger tips was used inancient Egypt and was alsoaccepted as a unit of length in otherparts of the world.

People also used the "foot" as aunit of length in different parts ofthe world. The length of the footused varied slightly from region toregion.

People measured a yard of clothby the distance between the end ofthe outstretched arm and their chin.The Romans measured with theirpace or steps.

In ancient India, small lengthmeasurements used were an angul(finger) or a mutthi (fist). Even today,we can see flower sellers using theirforearm as a unit of length forgarlands in many towns of India.Many such body parts continue tobe in use as unit of length, whenconvenient.

However, everyone's body couldbe of slightly different sizes. This

must have caused confusion inmeasurement. In 1790, the Frenchcreated a standard unit ofmeasurement called themetric system.

For the sake of uniformity,scientists all over the world haveaccepted a set of standard units ofmeasurement. The system of unitsnow used is known as theInternational System of Units (SIunits). The SI unit of length is ametre. A metre scale is shown inFig.10.6. Also shown is the 15 cmscale in your geometry box.

Each metre (m) is divided into100 equal divisions, calledcentimetre (cm). Each centimetrehas ten equal divisions, calledmillimetre (mm). Thus,

1 m = 100 cm1 cm = 10 mmFor measuring large distances,

metre is not a convenient unit. Wedefine a larger unit of length. It iscalled kilometre (km).

1 km = 1000 mNow, we can repeat all our

measurement activities using astandard scale and measure in SIunits. Before we do that, we do needto know the correct way ofmeasuring lengths and distances.

10.5 CORRECT MEASUREMENT OFLENGTH

In our daily life we use various typesof measuring devices. We use a

Fig.10.6 A metre scale and a 15 cm scale

100 SCIENCE

metre scale for measuring length. Atailor uses a tape, whereas a clothmerchant uses a metre rod. Formeasuring the length of an object,you must choose a suitable device.You cannot measure the girth of atree or the size of your chest using ametre scale, for instance. Measur-ing tape is more suitable for this. Forsmall measurements, such as thelength of your pencil, you can use a15 cm scale from your geometry box.

In taking measurement of alength, we need to take care of thefollowing:1. Place the scale in contact with the

object along its length as shownin Fig.10.7.

2. In some scales, the ends may bebroken. You may not be ableto see the zero mark clearly(Fig.10.8 (a)]. In such cases,you should avoid taking

measurements from the zeromark of the scale. You can useany other full mark of the scale,say, 1.0 cm [Fig.10.8 (b)]. Thenyou must subtract the reading ofthis mark from the reading at theother end. For example, inFig.10.8 (b) the reading at oneend is 1.0 cm and at the otherend it is 14.3 cm. Therefore, thelength of the object is (14.3-1.0)cm = 13.3 cm.

Fig. 10.7 Method of placing the scale alongthe length to be measured (a) correct and (b)incorrect

(a)

(b)

Fig. 10.8 (a) Incorrect and (b) correctmethod of placing the scale with broken

edge

(a)

(b)

3. Correct position of the eye is alsoimportant for taking measure-ment. Your eye must be exactlyin front of the point where themeasurement is to be taken asshown in Fig.10.9. Position 'B' isthe correct position of the eye.Note that from position 'B', thereading is 7.5 cm. From positions'A' and 'C', the readings may bedifferent.


Activity 3Measure the height of your classmateusing hand span and then by usinga metre scale. For this, ask yourclassmate to stand with his backagainst a wall. Make a mark on thewall exactly above his head. Now,measure the distance from the floorto this mark on the wall with yourhandspan and then with a metrescale. Let all other students measurethis length in a similar way. Recordall observations in Table 10.3.

Table 10.3 Measurement of

height

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Study carefully results obtainedby different students. The results incolumn 2 may be different fromeach other as the length of thehandspan may be different for

different students. Look at theresults in column 3 where themeasurements are done using astandard scale. The results may beclose to each other now, but, arethey exactly equal? If not, why doyou think there is a difference?After all, everybody is using thesame scale and not different handspans. This could be due to smallerrors in taking observations. Inhigher classes we will learn aboutthe importance of knowing andhandling such errors in measure-ment.

10.6 MEASURING THE LENGTH OFA CURVED LINE

We cannot measure the length of acurved line directly by using a metrescale. We can use a thread tomeasure the length of a curved line.

Activity 4

Use a thread to measure the lengthof the curved line AB (Fig.10.10).Put a knot on the thread near oneof its ends. Place this knot on thepoint A. Now, place a small portionof the thread along the line, keepingit taut using your fingers andthumbs. Hold the thread at this endpoint with one hand. Using the otherhand, stretch a little more portionof the thread along the curved line.

Fig. 10.9 B is the proper position of the

eye for taking reading of the scale

(A) (B) (C)

Fig.10.10 Measuring the length of acurved line with a thread

AB

102 SCIENCE

Go on repeating this process till theother end B of the curved line isreached. Make a mark on the threadwhere it touches the end B. Nowstretch the thread along a metrescale. Measure the length betweenthe knot in the beginning and thefinal mark on the thread. This givesthe length of the curved line AB.

We see that we need a lot of careto ensure that we are measuringdistances and lengths correctly.And, we need some standard unitsand devices with which we measurethese distances and can convey ourresults to others.

10.7 MOVING THINGS AROUND US

Activity 5Think of some objects you have seenrecently. List them in Table 10.4. Aschool bag, a mosquito, a table,people sitting on desks, people mov-ing about? May be a butterfly, dog,cow, your hand, a small baby, a fishin water, a house, a factory, a stone,a horse, a ball, a bat, a moving train,a sewing machine, a wall clock,hands of a clock? Make your list aslarge as you can.

Which of these are moving?Which are at rest?

How did you decide whether anobject is in motion or at rest?

You might have noticed that thebird is not at the same place aftersome time, while the table is at thesame place. On this basis you mayhave decided whether an object isat rest or in motion.

Let us look at the motion of anant closely.

Activity 6Spread a large sheet of white paperon the ground and keep a little sugaron it. Ants are likely to be attractedto the sugar and you will find manyants crawling on the sheet of papersoon. For any one ant, try and makea small mark with a pencil near itsposition when it has just crawled onto the sheet of paper (Fig. 10.11).Keep marking its position after a fewseconds as it moves along on thesheet of paper. After some time,shake the paper free of the sugarand the ants. Connect the differentpoints you have marked, witharrows, to show the direction in

Table10. 4 Objects in rest and

motion

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Fig. 10.11 Motion of an ant


you think of more such examplesfrom your surroundings ?

In all these examples we see thatthe objects move along a straightline. This type of motion is calledrectilinear motion.

Activity 7

Take a stone, tie a thread to it andwhirl it with your hand. Observe themotion of the stone. We see that thestone moves along a circular path.

In this motion, the distance of thestone from your hand remains thesame. This type of motion is calledcircular motion (Fig. 10.13).

which the ant was moving. Eachpoint you have marked shows wherethe ant moved to, in intervals of afew seconds.

Motion seems to be some kindof a change in the position of anobject with time, isn't it?

In Activity 5, where did you placeobjects like a clock, a sewingmachine or an electric fan in yourgrouping of objects? Are theseobjects moving from one place toother? No? Do you notice movementin any of their parts? The blades ofthe fan or the hands of aclock— how are they moving? Istheir movement similar to that of atrain? Let us now look at sometypes of motion to help us under-stand these different kind of move-ments.

10.8 TYPES OF MOTION

You may have observed the motionof a vehicle on a straight road,march-past of soldiers in a paradeor the falling of a stone (Fig. 10.12).What kind of motion is this ?

Sprinters ina 100-metrerace alsomove alonga straighttrack. Can

Fig.10.12 Some examples of rectilinearmotion

(a)

(b)

Fig. 10.13 Some objects in circular motion

(a)

(c)(b)

The motion of a point marked onthe blade of an electric fan or thehands of a clock are examples ofcircular motion.

The electric fan or the clock bythemselves are not moving from oneplace to another. But, the blades of

104 SCIENCE

played, are all examples of periodicmotion where an object repeats itsmotion after a fixed interval of time(Fig. 10.14).

Did you observe a sewingmachine as a part of Activity 5? Youmust have observed that it remainsat the same location while its wheelmoves with a circular motion. It alsohas a needle that moves up anddown continuously, as long as thewheel rotates, isn't it? This needleis undergoing a periodic motion.

Have you observed closely, themotion of a ball on the ground?

the fan rotateand so do thehands of aclock. If wemark a pointanywhere onthe blades of afan or on thehands of aclock, thedistance of thispoint from the

centre of the fan or the clock face,will remain the same as they rotate.

In some cases, an object repeatsits motion after some time. This typeof motion is called periodic motion.Take the stone tied with a string thatyou used in Activity 6. Now, hold thestring in your hand and let the stonehang from it. Pull the stone to oneside with the other hand and let itgo. This is a pendulum. Somethingto have a lot of fun with andsomething that will help usunderstand about periodic motion.Motion of a pendulum, a branch ofa tree moving to and fro, motion ofa child on a swing, strings of a guitaror the surface of drums (tabla) being

Boojho is not sure why we say that the

distance of the stone from your hand is

the same when we whirl it around. Can

you help him understand this?

Remember that the stone

is held with a string.

Fig. 10.14 Examples of periodic motion

(b) (c)

(d) (e)

(a)


Here, the ball is rolling on theground - rotating as well as movingforward on the ground. Thus, theball undergoes a rectilinear motionas well as rotational motion. Canyou think of other examples whereobjects undergo combinations ofdifferent types of motion?

We did many measurementactivities and discussed some kindsof motion. We saw that motion wasa change in the position of an objectwith time. The change in this

position can be determined throughdistance measurements. This allowsus to know how fast or slow a motionis. The movement of a snail on theground, a butter fly flittingfrom flower to flower, a river flowingalong on clear rounded pebbles, anaeroplane flying high up in theair — making jet trails, moongoing around the Earth, bloodflowing inside our bodies, there ismotion everywhere around us!

Different modes of transport are used to go from one place to another.

In ancient times, people used length of a foot, the width of a finger, thedistance of a step as units of measurement. This caused confusion anda need to develop a uniform system of measurement arose.

Now, we use International System of Unit ( SI unit). This is accepted allover the world.

Metre is the unit of length in SI unit.

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Key Words

Summary

106 SCIENCE

Motion in a straight line is called rectilinear motion.

In circular motion an object moves such that its distance from a fixedpoint remains the same.

Motion that repeats itself after some period of time, is called periodicmotion.


1. Draw a map of your classroom. Roll a ball on the floor. In your map mark thepoints where the ball started and where it stopped. Show also the path itmoved along. Did the ball move along a straight line?

2. Using string and a scale, let each student measure the length of his/her foot.Prepare a bar graph of the foot length measurements that have been obtainedfor the whole class.

1. Give two examples each, of modes of transport used on land, water and air.


(i) One metre is ______________ cm.

(ii) Five kilometre is ______________ m.

(iii)Motion of a child on a swing is ______________.

(iv)Motion of the needle of a sewing machine is ______________.

(v) Motion of wheel of a bicycle is______________.

3. Why can a pace or a footstep not be used as a standard unit of length?

4. Arrange the following lengths in their increasing magnitude:

1 metre, 1 centimetre, 1 kilometre,1 millimetre.

5. The height of a person is 1.65 m. Express it into cm and mm.

6. The distance between Radha's home and her school is 3250 m. Express thisdistance into km.

7. While measuring the length of a knitting needle, the reading of the scale at oneend is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?

8. Write the similarities and differences between the motion of a bicycle and aceiling fan that has been switched on.

9. Why could you not use an elastic measuring tape to measure distance? Whatwould be some of the problems you would meet in telling someone about adistance you measured with an elastic tape?

10. Give two examples of periodic motion.

Exercises

Light, Shadows andReflections11

We see so many objects aroundus, colourful anddifferent. On the way to

school we see things like buses, cars,cycles, trees, animals and sometimesflowers. How do you think, we seeall these objects?

Think of the same places at nighttime if it were completely dark. Whatwill you see? Suppose you go insidea completely dark room. Are you ableto see any objects in the room?

But, when you light a candle or atorch you can see the objectspresent in the room, isnt it? Withoutlight, things cannot be seen. Lighthelps us see objects.

The torch bulb is an object thatgives out light of its own. The Sun,is another familiar object that givesits own light. During the day, its lightallows us to see objects. Objects likethe sun that give out or emit light oftheir own are called luminousobjects.

What about objects like a chair, apainting or a shoe? We see thesewhen light from a luminous object(like the Sun, a torch or an electriclight) falls on these and then travelstowards our eye.

11.1 TRANSPARENT, OPAQUE AND

TRANSLUCENT OBJECTS

Recall our grouping objects asopaque, transparent or translucent,in Chapter 4. If we cannot see

through an object at all, it is anopaque object. If you are able to seeclearly through an object, it isallowing light to pass through it andis transparent. There are someobjects through which we can see,but not very clearly. Such objects areknown as translucent.

Activity 1Look around you and collect asmany objects as you can — an eraser,plastic scale, pen, pencil, notebook,single sheet of paper, tracing paperor a piece of cloth. Try to look atsomething far away, through each ofthese objects (Fig. 11.1). Is light froma far away object able to travel toyour eye, through any of the objects?

Record your observations in atable as shown in Table 11.1.

We see that a given object ormaterial could be transparent,

Fig. 11.1 Observing objects that do or donot allow light to pass through them.

108 SCIENCE

translucent or opaque depending onwhether it allows light to passthrough it completely, partially or notat all.

11.2 WHAT EXACTLY ARE SHADOWS?

Activity 2Now, one by one hold each of theopaque objects in the sunlight,slightly above the ground. What doyou see on the ground ? You knowthat the dark patch formed by eachon the ground is due to its shadow.Sometimes you can identify the objectby looking at its shadow (Fig. 11.2).

Spread a sheet of paper on theground. Hold a familiar opaque objectat some height, so that its shadow isformed on the sheet of paper on theground. Ask one of your friends todraw the outline of the shadow while

you are holding the object. Drawoutlines of the shadows of otherobjects in a similar way.

Now, ask some other friends toidentify the objects from theseoutlines of shadows. How manyobjects are they able to identifycorrectly?

Do you observe your shadow in adark room or at night when there isno light? Do you observe a shadowwhen there is just a source of lightand nothing else, in a room? It seemswe need a source of light and anopaque object, to see a shadow. Isthere anything else required?

Activity 3This is an activity that you will haveto do in the dark. In the evening, goout in an open ground with a fewfriends. Take a torch and a largesheet of cardboard with you. Holdthe torch close to the ground andshine it upwards so that its light fallson your friend's face. You now havea source of light that is falling on anopaque object. If there were no trees,building or any other object behindyour friend, would you see theshadow of your friend's head? Thisdoes not mean that there is noshadow. After all, the light from the

Table 11.1

lairetam/tcejbOtcejboehthguorhtweiV/yllaitrap/ylluf(elbissop

)llataton

/euqapositcejbO/tnerapsnarttneculsnart

licneP

llabrebbuR

repapgnitirwfoteehS ?erusyrevtoN

Fig. 11.2 Sometimes shadow of an objectgives an idea about its shape

109LIGHT, SHADOWS AND REFLECTIONS

torch is not able to pass through hisbody to the other side.

Now, ask another friend to holdthe cardboard sheet behind yourfriend. Is the shadow now seen onthe cardboard sheet (Fig. 11.3)?

Thus, the shadow can be seenonly on a screen. The ground, wallsof a room, a building, or other suchsurfaces act as a screen for theshadows you observe in everyday life.

Shadows give us some informationabout shapes of objects. Sometimes,shadows can also mislead us aboutthe shape of the object. In Fig. 11.4are a few shadows that we can createwith our hands and make-believe thatthey are shadows of different animals.Have fun!

Activity 4Place a chair in the school groundon a sunny day. What do you observefrom the shadow of the chair?

Does the shadow give an accuratepicture of the shape of the chair? Ifthe chair is turned around a little,how does the shape of the shadowchange?

Take a thin notebook and look atits shadow. Then, take a rectangularbox and look at its shadow. Do thetwo shadows seem to have a similarshape?

Take flowers or other objects ofdifferent colours and look at theirshadows. A red rose and a yellowrose, for instance. Do the shadowslook different in colour, when thecolours of the objects are different?

Take a long box and look at itsshadow on the ground. When youmove the box around, you may seethat the size of the shadow changes.When is the shadow of the box theshortest, when the long side of thebox is pointed towards the Sun orwhen the short side is pointingtowards the Sun?

Let us use this long box, toprepare a simple camera.

Fig. 11.3 A shadow is obtained only on ascreen

Fig 11.4 Shadows of animals hidden in yourhand

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11.3 A PINHOLE CAMERA

Surely we need a lot of complicatedstuff to make a camera? Not really. Ifwe just wish to make a simple pinhole camera.

Activity 5Take two boxes so that one can slideinto another with no gap in betweenthem. Cut open one side of each box.On the opposite face of the larger box,make a small hole in the middle[Fig. 11.5 (a)]. In the smaller box, cutout from the middle a square with aside of about 5 to 6 cm. Cover this opensquare in the box with tracing paper(translucent screen) [Fig. 11.5 (b)].Slide the smaller box inside thelarger one with the hole, in such away that the side with the tracingpaper is inside [Fig. 11.5 (c)]. Yourpin hole camera is ready for use.

Holding the pin hole camera lookthrough the open face of the smallerbox. You should use a piece of blackcloth to cover your head and thepinhole camera. Now, try to look atsome distant objects like a tree or abuilding through the pinholecamera. Make sure that the objectsyou wish to look at through your

pinhole camera are in bright sunshine. Move the smaller box forwardor backward till you get a picture onthe tracing paper pasted at the otherend.

Are these pin hole imagesdifferent from their shadows?

Look through your pin holecamera at the vehicles and peoplemoving on the road in bright sunlight.

Do the pictures seen in the camerashow the colours of the objects onthe other side? Are the images erector upside down? Surprise, surprise!

Let us now image the Sun, withour pin hole camera. We need aslightly different set up for this. Wejust need a large sheet of cardboardwith a small pin hole in the middle.Hold the sheet up in the Sun and letits shadow fall on a clear area. Doyou see a small circular image of theSun in the middle of the shadow ofthe cardboard sheet?

Look at these pin hole images ofthe Sun when an eclipse is visiblefrom your location. Adjust your pinhole and screen to get a clear imagebefore the eclipse is to occur. Look

(a) (b) (c)

Fig. 11.5 A sliding pin hole camera


at the image as the eclipse begins.You will notice a part of the Sun'simage gradually becoming darker asthe eclipse starts. Never ever lookdirectly at the Sun. That could beextremely harmful for the eyes.

There is an interesting pin holecamera in Nature. Sometimes, whenwe pass under a tree covered withlarge number of leaves, we noticesmall patches of sun light under it(Fig. 11.6). These circular images are,in fact, pin hole images of the Sun.The gaps between the leaves, act asthe pin holes. These gaps are allkinds of irregular shapes, but, we cansee circular images of the Sun. Tryto locate images of the Sun when an

Paheli has another thought.Surely, all these results that we areseeing, formation of shadows andpinhole images are possible only iflight moves in a straight path?

Activity 6Let us use a piece of a pipe or a longrubber tube. Light a candle and fix iton a table at one end of the room. Nowstanding at the other end of the roomlook at the candle through the pipe

Fig. 11.6 A natural pinhole camera. Pinhole

images of the Sun under a tree!

eclipse occurs next. That could be somuch fun!

Boojho has this thought. We sawupside down images of people on theroad, with our pinhole camera. Whatabout the images of the Sun? Didwe notice them to be upside down oranything like that?

Fig. 11.7 Looking through a pipe pointed(a) towards and (b) a little away from a candle

(a)

(b)

[Fig. 11.7 (a)]. Is the candle visible?Bend the pipe a little while you arelooking at the candle [Fig. 11.7 (b)].Is the candle visible now? Turn thepipe a little to your right or left. Canyou see the candle now?

What do you conclude from this?This suggests that light travels

along a straight line, isn’t it? That iswhy, when opaque objects obstructit, a shadow forms.

112 SCIENCE

11.4 MIRRORS AND REFLECTIONS

We all use mirrors at home. You lookinto the mirror and see your own faceinside the mirror. What you see is areflection of your face in the mirror.We also see reflections of other objectsthat are in front of the mirror.Sometimes, we see reflections of trees,buildings and other objects in thewater of a pond or a lake.

Activity 7This activity should be done at nightor in a dark room. Ask one of yourfriends to hold a mirror in his/herhand at one corner of the room. Standat another corner with a torch in yourhand. Cover the glass of torch withyour fingers and switch it on. Adjustyour fingers with a small gap betweenthem so that you can get a beam oflight. Direct the beam of the torch lightonto the mirror that your friendis holding. Do you see a patch oflight on the other side (Fig. 11.8)?

Now, adjust the direction of the torchso that the patch of light falls onanother friend standing in the room.

This activity suggests that amirror changes the direction of lightthat falls on it.

Here is an activity that shows lighttravelling along straight lines andgetting reflected from a mirror.

Activity 8Fix a comb on one side of a largethermocol sheet and fix a mirror onthe other side as shown in Fig. 11.9.Spread a dark coloured sheet ofpaper between the mirror and thecomb. Keep this in sunlight or senda beam of light from a torch throughthe comb.

What do you observe? Do you geta pattern similar to that shownin Fig. 11.9?

This activity gives us an idea ofthe manner in which light travelsand gets reflected from a mirror.

Fig. 11.8 A mirror reflects a beam of lightFig. 11.9 Light travelling in a straight line

and getting reflected from a mirror


Opaque objects do not allow light to pass through them.

Transparent objects allow light to pass through them and we can seethrough these objects clearly.

Translucent objects allow light to pass through them partially.

Shadows are formed when an opaque object comes in the path of light.

Pinhole camera can be made with simple materials and can be used toimage the Sun and brightly lit objects.

Mirror reflection gives us clear images.

Images are very different from shadows.

Light travels in straight line.

1. Rearrange the boxes given below to make a sentence that helps us understandopaque objects.

suonimuL

rorriM

euqapO

aremacelohniP

noitcelfeR

wodahS

tneculsnarT

tnerapsnarT

O W S A K E O P A Q U E O B J E C T S M

S H A D

Summary

Exercises

Key Words

114 SCIENCE

Fig. 11.10

2. Classify the objects or materials given below as opaque, transparent or translucentand luminous or non-luminous:

Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden board, a sheet ofpolythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, anumbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the flame of agas burner, a sheet of cardboard, a lighted torch, a sheet of cellophane, a wire mesh,kerosene stove, sun, firefly, moon.

3. Can you think of creating a shape that would give a circular shadow if held in oneway and a rectangular shadow if held in another way?

4. In a completely dark room, if you hold up a mirror in front of you, will you see areflection of yourself in the mirror?

SUGGESTED ACTIVITIES

1. Make a row of your friends — A, B, C and D, standing in a line. Let one friend stand infront facing them and holding out a mirror towards them (Fig. 11.10).

Now, each person can tell who they are able to see in the Mirror. A,B, C, or D.

If, A is able to see B in the mirror then, can B also see A in the mirror? Similarly, forany two pairs amongst A,B,C, or D?

If A is not able to see B in the mirror, then, is B able to see A in the mirror?

Similarly, for any two pairs amongst A,B,C, or D?

This activity tells us something about the way light travels and gets reflected frommirrors. You will learn more about this in higher classes.

2. Daayan-Baayan—Take a comb in your right hand and bring it up to your hair andlook at yourself in the mirror. There is your familiar face, grinning at you

Wait, try and find out which is the hand holding the comb, in your mirror reflection.Is it the right hand or the left? You were holding it in your right hand, isn't it?

While a pin hole camera seems to be giving us upside down images, a mirror seemsto be turning right hand into left hand and the left into right hand. We will learnmore about this in the higher classes.


Fig. 11.11 Seeing around corners!

Mirror 1

Mirror 2Fig. 11.12 A periscope

3. Magic Device—In the chapter onsymmetry in your Mathematicstextbook, you might have made aninteresting device Kaleidoscope, thatuses reflections. Now, let us makeanother device, a periscope, that usesreflections to see around corners! Askone of your freinds to stand in thecorridor just out side the entrance tothe classroom with a mirror in hand.Ask another friend also holding amirror, to stand in the middle ofclassroom in front of the entrance. Nowask your friends to ajust their mirrorsin such a way that the image of object on the other side of the corridor becomesvisible to you while you are standing inside the class (Fig. 11.11).

You can make a simple periscope by placing two mirrors in a ‘Z’ shaped box asshown in Fig. 11.12.


1. Opaque objects cast shadows, isn't it? Now, if we hold a transparent object inthe Sun, do we see anything on the ground that gives us a hint that we areholding something in our hand?

2. We saw that changing colour of opaque objects does not change the colour oftheir shadows. What happens if we place an opaque object in coloured light?You can cover the face of a torch with a coloured transparent paper to do this.(Did you ever noticed the colours of evening shadows just as the Sun is setting?)

THINGS TO READ

Rudyard Kipling's "Just So Stories" and in particular, the story of "How the Leopardgot its spots" where he mentions stripy, speckly, patchy-blatchy shadows. Hereare a few lines from this story, that has a lot of shadows.

...after ever so many days, they saw a great, high, tall forest full of tree trunksall 'sclusively speckled and sprottled and spottled, dotted and splashed andslashed and hatched and cross-hatched with shadows. (Say that quickly aloud,and you will see how very shadowy the forest must have been.)

'What is this,' said the Leopard, 'that is so 'sclusively dark, and yet so full oflittle pieces of light?'

Electricity and Circuits12We use electricity for many

purposes to make our taskseasier. For example, we

use electricity to operate pumps thatlift water from wells or from groundlevel to the roof top tank. What areother purposes for which you useelectricity? List some of them in yournotebook.

Does your list include the use ofelectricity for lighting? Electricitymakes it possible to light our homes,roads, offices, markets and factorieseven after sunset. This helps us tocontinue working at night. A powerstation provides us with electricity.However, the supply of electricity mayfail or it may not be available at someplaces. In such situations, a torch issometimes used for providing light. Atorch has a bulb that lights up whenit is switched on. Where does the torchget electricity from?

12.1. ELECTRIC CELL

Electricity to the bulb in a torch is

provided by the electric cell. Electriccells are also used in alarm clocks,wristwatches, transistor radios,cameras and many other devices.Have you ever carefully looked at anelectric cell? You might have noticedthat it has a small metal cap on oneside and a metal disc on the otherside (Fig. 12.1). Did you notice apositive (+) sign and a negative (–)sign marked on the electric cell? Themetal cap is the positive terminal ofthe electric cell. Themetal disc is thenegative terminal. Allelectric cells have twoterminals; a positiveterminal and a negativeterminal.

An electric cell produceselectricity from the chemicals storedinside it. When the chemicals in theelectric cell are used up, the electriccell stops producing electricity. Theelectric cell then has to be replacedwith a new one.

Fig.12.1 AnElectric Cell

You might have seen the danger sign shown here displayed on poles,electric substations and many other places. It is to warn people thatelectricity can be dangerous if not handled properly. Carelessnessin handling electricity and electric devices can cause severe injuriesand sometimes even death. Hence, you should never attempt toexperiment with the electric wires and sockets. Also remember thatthe electricity generated by portable generators is equally dangerous.Use only electric cells for all activities related to electricity.

Caution

117ELECTRICITY AND CIRCUITS

A torch bulb has an outer case ofglass that is fixed on a metallic base[Fig. 12. 2 (a)]. What is inside theglass case of the bulb?

Activity 1Take a torch and look inside its bulb.You can also take out the bulb withthe help of your teacher. What do younotice? Do you find a thin wire fixedin the middle of the glass bulb[Fig. 12.2 (b)]? Now switch the torchon and observe which part of the bulbis glowing.

The thin wire that gives off light iscalled the filament of the bulb. Thefilament is fixed to two thicker wires,which also provide support to it, asshown in Fig. 12.2 (b). One of these thickwires is connected to the metal case atthe base of the bulb [Fig. 12.2 (b)].The other thick wire is connected tothe metal tip at the centre of the base.The base of the bulb and the metaltip of the base are the two terminalsof the bulb. These two terminals arefixed in such a way that they do not

touch each other. The electric bulbsused at home also have a similardesign.

Thus, both the electric cell andthe bulb have two terminals each.Why do they have these twoterminals?

12.2. A BULB CONNECTED TO ANELECTRIC CELL

Let us try to make an electric bulblight up using an electric cell. Howdo we do that?

Activity 2Take four lengths of electric wire withdifferently coloured plastic coverings.Remove a little of the plastic coveringfrom each length of wire at the ends.This would expose the metal wiresat the ends of each length. Fix theexposed parts of the wires to the celland the bulb as shown in Fig 12.3and Fig. 12.4.

Fig.12.2 (a) Torch bulb and (b) itsinside view

Filament

Terminals

(a) (b)

Caution: Never join the twoterminals of the electric cell withoutconnecting them through a switchand a device like a bulb. If you doso, the chemicals in the electric cellget used up very fast and the cellstops working.

Fig.12.3 Electric cell with two wiresattached to it

118 SCIENCE

You can stick the wires to the bulbwith the tape used by electricians.Use rubber bands or tape to fix thewires to the cell.

Now, connect the wires fixed to thebulb with those attached to the cellin six different ways as has beenshown in Fig. 12.5 (a) to (f). For eacharrangement, find out whether the

bulb glows or not. Write 'Yes' or 'No'for each arrangement in yournotebook.

Now, carefully look at thearrangements in which the bulbglows. Compare these with thosein which the bulb does not glow.Can you find the reason for thedifference?

Keep the tip of your pencil on thewire near one terminal of the electriccell for the arrangment in Fig. 12.5(a)Move the pencil along the wire all theway to the bulb. Now, from the otherterminal of the bulb, move along theother wire connected to the cell.Repeat this exercise for all the otherarrangements in Fig. 12.5. Did thebulb glow for the arrangements inwhich you could not move the pencilfrom one terminal to the other?

Fig.12.4 Bulb connected to two wires

(d) (e) ( f )

Fig.12.5 Different arrangements of electric cell and bulb

(a) (b) (c)


12.3 AN ELECTRIC CIRCUIT

In Activity 2 you connected oneterminal of the electric cell to theother terminal through wires passingto and from the electric bulb. Notethat in the arrangements shown inFig. 12. 5 (a) and (f), the two terminalsof the electric cell were connected totwo terminals of the bulb. Such anarrangement is an example of anelectric circuit. The electric circuitprovides a complete path forelectricity to pass (current to flow)between the two terminals of theelectric cell. The bulb glows onlywhen current flows through thecircuit.

In an electric circuit, the directionof current is taken to be from thepositive to the negative terminal ofthe electric cell as shown in Fig.12.6.When the terminals of the bulb areconnected with that of the electric cellby wires, the current passes through

has fused. Look at a fused bulbcarefully. Is the filament inside itintact?

An electric bulb may fuse due tomany reasons. One reason for a bulbto fuse is a break in its filament. Abreak in the filament of an electricbulb means a break in the path ofthe current between the terminals ofthe electric cell. Therefore, a fusedbulb does not light up as no currentpasses through its filament.

Can you now explain why thebulb did not glow when you tried todo so with the arrangements shownin Fig. 12.5 (b), (c), (d) and (e)?

Now we know how to make a bulblight up using an electric cell. Wouldyou like to make a torch for yourself?

Activity 3Take a torch bulb and a piece of wire.Remove the plastic covering at thetwo ends of the wire as you didbefore. Wrap one end of a wirearound the base of an electric bulbas shown in Fig. 12.7. Fix the otherend of the wire to the negativeterminal of an electric cell with a

Fig.12.6 Direction of current in an electriccircuit

the filament of the bulb. This makesthe bulb glow.

Sometimes an electric bulb doesnot glow even if it is connected tothe cell. This may happen if the bulb Fig. 12.7 A home made torch

120 SCIENCE

rubber band. Now, bring the tip ofthe base of the bulb that is, its otherterminal, in contact with the positiveterminal of the cell. Does the bulbglow? Now move the bulb away fromthe terminal of the electric cell. Doesthe bulb remain lighted? Is this notsimilar to what you do when youswitch your torch on or off?

12.4 ELECTRIC SWITCH

We had an arrangement for switchingon or off our home made torch bymoving the base of the bulb awayfrom the tip of the cell. This was asimple switch, but, not very easy touse. We can make another simpleand easier switch to use in ourcircuit.

Activity 4You can make a switch using twodrawing pins, a safety pin (or a paper

clip), two wires and a small sheet ofthermocol or a wooden board. Inserta drawing pin into the ring at oneend of the safety pin and fix it on thethermocol sheet as shown in Fig. 12.8.Make sure that the safety pin can berotated freely. Now, fix the otherdrawing pin on the thermo Col sheetin a way that the free end of thesafety pin can touch it. The safetypin fixed in this way would be yourswitch in this activity.

Fig 12.9 An electric circuit with a switch

Paheli has anotherarrangement of the celland the bulb. Will thetorch bulb glow inthe followingarrangement?

Fig. 12.8 A simple switch

Now, make a circuit by connect-ing an electric cell and a bulb withthis switch as shown in Fig.12.9.Rotate the safety pin so that its freeend touches the other drawing pin.What do you observe? Now, move thesafety pin away. Does the bulbcontinue to glow?

The safety pin covered the gapbetween the drawing pins whenyou made it touch two of them. Inthis position the switch is said to be'on' (Fig. 12.10). Since the materialof the safety pin allows the currentto pass through it, the circuit wascomplete. Hence, the bulb glows.

Fig. 12.10 A switch in ‘on’ position


On the other hand, the bulb didnot glow when the safety pin was notin touch with the other drawing pin.The circuit was not complete as therewas a gap between the two drawing

Fig. 12.11 Inside view of a torch

Boojho has drawn theinside of the torch as inFig. 12.11. When we closethe switch, the circuit iscompleted and the bulb

glows. Can you draw a red lineon the figure indicating thecomplete circuit?

Reflec-tor

pins. In this position, the switch issaid to be 'off' as in Fig. 12.9.

A switch is a simple device thateither breaks the circuit or completesit. The switches used in lighting ofelectric bulbs and other devices inhomes work on the same principlealthough their designs are morecomplex.

12.5 ELECTRIC CONDUCTORS ANDINSULATORS

In all our activities we have usedmetal wires to make a circuit.Suppose we use a cotton threadinstead of a metal wire to make acircuit. Do you think that the bulbwill light up in such a circuit? Whatmaterials can be used in electriccircuits so that the current can passthrough them? Let us find out.

Activity 5Disconnect the switch from the electriccircuit you used for Activity 4. Thiswould leave you with two free ends ofwires as shown in Fig. 12.12 (a). Bringthe free ends of the two wires close, tolet them touch each other. Does thebulb light up? You can now use thisarrangement to test whether any givenmaterial allows current to passthrough it or not.

Fig. 12.12 (a) A conduction tester(b) Testing whether the bulb glows when the

tester is in contact with a key

(a) (b)

122 SCIENCE

Collect samples of different typesof materials such as coins, cork,rubber, glass, keys, pins, plasticscale, wooden block, pencil lead,aluminium foil, candle, sewingneedle, thermo Col, paper and pencillead. One by one bring the free endsof the wires of your tester in contactwith two ends of the samples youhave collected [Fig. 12.12 (b)]. Makesure that the two wires do not toucheach other while you are doing so.Does the bulb glow in each case?

Make a table in your notebooksimilar to Table.12.1, and record yourobservations.

Table 12.1 Conductors andinsulators

nidesutcejbOehtfoecalp

hctiws

lairetaMsiti

foedam

bluB?swolg

)oN/seY(

yeK lateM seY

resarE rebbuR oN

elacS citsalP

kcitshctaM dooW

elgnabssalG ssalG

liannorI lateM

What do you find? The bulb doesnot glow when the free ends of thewires are in contact with some of thematerials you have tested. This meansthat these materials do not allow theelectric current to pass through them.On the other hand, some materialsallow electric current to pass throughthem, which is indicated by theglowing bulb. Materials whichallow electric current to pass through

them are conductors of electricity.Insulators do not allow electric currentto pass through them. With the helpof Table 12.1, name the materialsthat are conductors of electricity andalso those which are insulators.Conductors ______, ______, _________Insulator _________, _______, ________

What do you conclude? Whichmaterials are conductors and whichare insulators? Recall the objects thatwe grouped as those havinglustre, in Chapter 4. Are they theconductors? It now seems easy tounderstand why copper, aluminumand other metals are used formaking wires.

Let us recall Activity 4 in whichwe made an electric circuit with aswitch (Fig.12.9). When the switchwas in the open position, were thetwo drawing pins not connected witheach other through the thermocolsheet? But, thermocol, you may havefound is an insulator. What aboutthe air between the gap? Since thebulb does not glow when there isonly air in the gap between thedrawing pins in your switch, itmeans that air is also an insulator.

Conductors and insulators areequally important for us. Switches,electrical plugs and sockets are madeof conductors. On the other hand,rubber and plastics are used forcovering electrical wires, plug tops,switches and other parts of electricalappliances, which people mighttouch.

Caution: Your body is a conductorof electricity. Therefore, be carefulwhen you handle an electricalappliance.


Electric cell is a source of electricity. An electric cell has two terminals; one is called positive (+ ve) while the

other is negative (– ve). An electric bulb has a filament that is connected to its terminals. An electric bulb glows when electric current passes through it. In a closed electric circuit, the electric current passes from one terminal

of the electric cell to the other terminal. Switch is a simple device that is used to either break the electric circuit or

to complete it. Materials that allow electric current to pass through them are called

conductors. Materials that do not allow electric current to pass through them are

called insulators.

tnemaliF

rotalusnI

hctiwS

lanimreT

Fig. 12.13

bluB

srotcudnoC

lleccirtcelE

tiucriccirtcelE

1. Fill in the blanks :

(a) A device that is used to break an electric circuit is called _______________.

(b) An electric cell has ____________________ terminals.

2. Mark 'True' or 'False' for following statements:

(a) Electric current can flow through metals.

(b) Instead of metal wires, a jute string can be usedto make a circuit.

(c) Electric current can pass through a sheetof thermo Col.

3. Explain why the bulb would not glow in thearrangement shown in Fig. 12.13.

Key Words

Exercises

Summary

124 SCIENCE

Fig. 12.15

4. Complete the drawing shown in Fig 12.14 toindicate where the free ends of the two wiresshould be joined to make the bulb glow.

5. What is the purpose of using an electric switch?Name some electrical gadgets that have switchesbuilt into them.

6. Would the bulb glow after completing the circuitshown in Fig. 12.14 if instead of safety pin weuse an eraser?

7. Would the bulb glow in the circuit shown in Fig. 12.15? Fig. 12.14

8. Using the "conduction tester" on an object it was found that the bulb begins toglow. Is that object a conductor or an insulator? Explain.

9. Why should an electrician use rubber gloves while repairing an electric switch atyour home? Explain.

10. The handles of the tools like screwdrivers and pliers used by electricians for repairwork usually have plastic or rubber covers on them. Can you explain why?

SOME SUGGESTED ACTIVITIES

1. Imagine there were no electric supply for a month. How would that affectyour day to day activities and others in your family? Present your imaginationin the form of a story or a play. If possible stage the play written by you oryour friends in school.

2. For your friends, you may set up a game "How steady is your hand?". You willneed a cell, an electric bulb, a metal key, two iron nails ( about 5 cm inlength), about one and a half metre long thick metal wire (with its plasticinsulation scraped off ) and few pieces of connecting wires. Fix two nailsnearly one metre apart on a wooden board so that these can be used as ahook. Fix the wire between the nails after inserting it through the loop of thekey. Connect one end of this wire to a bulb and a cell. Connect the otherterminal of the cell to the key with a wire. Ask your friend to move the loopalong the straight wire without touching it. Glowing of the bulb would indicatethat the loop of the key has touched the wire.

3. Read and find out about Alessandro Volta who invented the electric cell. Youmay also find out about Thomas Alva Edison who invented the electric bulb.

Fun with Magnets13Paheli and Boojho went to a

place where a lot of wastematerial was piled into huge

heaps. Something exciting washappening! A crane was movingtowards the heap of junk. The longhand of the crane lowered a blockover a heap. It then began to move.Guess, what? Many pieces of ironjunk were sticking to the block, as itmoved away (Fig. 13.1)!

They had just read a veryinteresting book on magnets andknew immediately that there mustbe a magnet attached to the end ofthe crane that was picking up ironfrom the junk yard.

You might have seen magnets andhave even enjoyed playing withthem. Have you seen stickers thatremain attached to iron surfaceslike almirahs or the doors of

refrigerators? In some pin holders,the pins seem to be sticking to theholder. In some pencil boxes, thelid fits tightly when we close it evenwithout a locking arrangement.Such stickers, pin holders andpencil boxes have magnets fittedinside (Fig. 13.2). If you have anyone of these items, try to locate themagnets hidden in these.

How Magnets Were DiscoveredIt is said that, there was a shepherdnamed Magnes, who lived in ancientGreece. He used to take his herd ofsheep and goats to the nearbymountains for grazing. He wouldtake a stick with him to control hisherd. The stick had a small piece ofiron attached at one end. One dayhe was surprised to find that he hadto pull hard to free his stick from a

Fig. 13.1 Picking up pieces of iron fromwaste

Fig. 13.2 Some common items that havemagnets inside them

126 SCIENCE

rock on the mountainside (Fig. 13.3).It seemed as if the stick was beingattracted by the rock. The rock wasa natural magnet and it attracted theiron tip of the shepherd's stick. It issaid that this is how naturalmagnets was discovered. Such rockswere given the name magnetite,perhaps after the name of thatshepherd. Magnetite contains iron.Some people believe that magnetitewas first discovered at a place calledMagnesia. The substances having theproperty of attracting iron are nowknown as magnets. This is how thestory goes.

In any case, people now havediscovered that certain rocks have theproperty of attracting pieces of iron.They also found that small pieces ofthese rocks have some specialproperties. They named thesenaturally occurring materialsmagnets. Later on the process ofmaking magnets from pieces of ironwas discovered. These are known asartificial magnets. Nowadays artificialmagnets are prepared in different

shapes. For example, bar magnet,horse-shoe magnet, cylindrical or aball-ended magnet. Fig.13.4 showsa few such magnets.

Activity 1

Take a plastic or a paper cup. Fix iton a stand with the help of a clampas shown in Fig. 13.5. Place a mag-net inside the cup and cover it witha paper so that the magnet is notvisible. Attach a thread to a clipmade of iron. Fix the other end ofthe thread at the base of the stand.(Mind you, the trick involved here,is to keep the length of the threadsufficiently short.) Bring the clip nearthe base of the cup. The clip is raisedin air without support, like a kite.

Fig.13.3 A natural magnet on a hillside!

Fig. 13.4 Magnets of different shapes

Fig. 13.5 Effect of magnet - a paper cliphanging in air!

127FUN WITH MAGNETS

13.1 MAGNETIC AND NON-MAG-NETIC MATERIALS

Activity 2Let us walk in the footsteps ofMagnes. Only, this time, we willchange the positions of the magnetand the iron. There will be a magnetat the end of our shepherd's stick.We can attach a small magnet to ahockey stick, walking stick or acricket wicket with a tape orsome glue. Let us now go out on a"Magnes walk" through the schoolplayground. What does our "Magnesstick" pick up from the schoolground? What about objects in theclassroom?

Collect various objects of day-to-day use from your surroundings.Test these with the "Magnes stick".You can also take a magnet, touchthese objects with it and observewhich objects stick to the magnet.Prepare a table in your notebook asshown in Table 13.1. and record yourobservations.

Look at the last column of Table13.1 and note the objects that areattracted by a magnet. Now, make a

list of materials from which theseobjects are made. Is there anymaterial common in all the objectsthat were attracted by the magnet?

We understand that magnetattracts certain materials whereassome do not get attracted towardsmagnet. The materials whichget attracted towards a magnetare magnetic – for example, iron,nickel or cobalt. The materialswhich are not attracted towards amagnet are non-magnetic. Whatmaterials did you find to be non-magnetic from Table 13.1? Is soil amagnetic or a non-magneticmaterial?

Boojho has this question for you.

A tailor was stitching buttons onhis shirt. The needle hasslipped from his hand on tothe floor. Can you help the

tailor to find the needle?

Table 13.1 Finding the objects attracted by magnet

foemaNtcejboeht

foedamsitcejboehthcihwlairetaM/doow/muinimula/citsalp/htolC(

rehtoyna/nori/ssalg

sengaMybdetcarttAtengam/kcits

)oN/seY(

llabnorI norI seY

elacS citsalP oN

eohS rehtaeL ?

128 SCIENCE

Activity 3Rub a magnet in the sand or soil.Pull out the magnet. Are there someparticles of sand or soil sticking tothe magnet? Now, gently shake themagnet to remove the particles ofsand or soil. Are some particles stillsticking to it? These might be smallpieces of iron (iron filings) picked upfrom the soil.

Through such an activity, we canfind out whether the soil or sandfrom a given place contains particlesthat have iron. Try this activity nearyour home, school or the places youvisit on your holidays. Does themagnet with iron filings sticking toit, look like any one of those shownin Fig. 13.6?

Make a table of what you find.

Fig. 13.6 Magnet with (a) many iron filings(b) few iron filings and

(c) no iron filings sticking to it.

(a)

(b)

(c)

If you fill this table and send it toPaheli and Boojho, they can comparethe amount of iron filings found insoil from different parts of thecountry. They can share thisinformation with you.

13.2 POLES OF MAGNET

We observed that iron filings (if theyare present) stick to a magnet rubbedin the soil. Did you observe anythingspecial about the way they stick tothe magnet?

Activity 4Spread some iron filings on a sheet ofpaper. Now, place a bar magnet onthis sheet. What do you observe? Dothe iron filings stick all over themagnet? Do you observe that moreiron filings get attracted to some partsof the magnet than others (Fig. 13.7)?Remove the iron filings sticking to themagnet and repeat the activity. Do youobserve any change in the pattern withwhich the iron filings get attracted bydifferent parts of the magnet? You can

Table 13.2 Magnet rubbed insand. How many iron filings?

noitacolfoemaNdnaynoloC(/ytic/nwot

)egalliv

noridnifuoydiDotgnikcitssgnilif

?tengameht/wefyrev/ynaM(

)enon

Fig. 13.7 Iron filings sticking to a barmagnet

do this activity using pins or iron nailsin place of iron filings and also withmagnets of different shapes.

Draw a diagram to show the wayiron filings stick to the magnet. Is yourdrawing similar to that shown inFig. 13.6 (a)?

129FUN WITH MAGNETS

We find that most of the iron filingsare attracted towards the two ends ofa bar magnet. These ends are thepoles of the magnet. Try and bring afew magnets of different shapes to theclassroom. Check for the location ofthe poles on these magnets using ironfilings. Can you now mark the locationof poles in the kind of magnets shownin Fig. 13.4?13.3 FINDING DIRECTIONS

Magnets were known to people fromancient times. Many properties ofmagnets were also known to them.You might have read many interestingstories about the uses of magnets.One such story is about an emperorin China named Hoang Ti. It is saidthat he had a chariot with a statue ofa lady that could rotate inany direction. It had an extended armas if it was showing the way(Fig.13.8).The statue had aninteresting property. It would rest insuch a position that its extended armalways pointed towards South. Bylooking at the extended arm of thestatue, the Emperor was able tolocate directions when he went tonew places on his chariot.

Let us make such a directionfinder for ourselves.

Activity 5Take a bar magnet. Put a mark onone of its ends for identification. Now,tie a thread at the middle of themagnet so that you may suspend itfrom a wooden stand (Fig. 13.9).Make sure that the magnet canrotate freely. Let it come to rest. Marktwo points on the ground to showthe position of the ends of the magnet

Paheli has this puzzle foryou. You are given two identicalbars which look as if they mightbe made of iron. One of them isa magnet, while the other is asimple iron bar. Howwill you find out, whichone is a magnet?

Fig. 13.8 The chariot with direction findingstatue

Fig. 13.9 A freely suspended bar magnetalways comes to rest in the same direction

130 SCIENCE

when it comes to rest. Draw a linejoining the two points. This lineshows the direction in which themagnet was pointing in its positionof rest. Now, rotate the magnet bygently pushing one end in anydirection and let it come to rest.Again, mark the position of the twoends in its position of rest. Does themagnet now point in a differentdirection? Rotate the magnet inother directions and note the finaldirection in which it comes to rest.

Do you find that the magnetalways comes to rest in the samedirection? Now can you guess themystery behind the statue in theEmperor's chariot?

Repeat this activity with an ironbar and a plastic or a wooden scaleinstead of a magnet. Do not use lightobjects for this activity and avoiddoing it where there are currents ofair. Do the other materials alsoalways come to rest in the samedirection?

We find that a freely suspendedbar magnet always comes to rest ina particular direction, which is theNorth-South direction. Use thedirection of the rising sun in themorning to find out the roughdirection towards east, where youare doing this experiment. If youstand facing east, to your left will beNorth. Using the Sun for findingdirections may not be very exact, but,it will help to make out the directionNorth from the South, on your line.Using this you can figure out whichend of the magnet is pointing to theNorth and which points to theSouth.

The end of the magnet that pointstowards North is called its North

seeking end or the North pole of themagnet. The other end that pointstowards the South is called Southseeking end or the South pole of themagnet. All magnets have two poleswhatever their shape may be. Usually,north (N) and south (S) poles aremarked on the magnets.

This property of the magnet isvery useful for us. For centuries,travellers have been making use ofthis property of magnets to finddirections. It is said that in oldendays, travellers used to finddirections by suspending naturalmagnets with a thread, which theyalways carried with them.

Later on, a device was developedbased on this property of magnets.It is known as the compass. Acompass is usually a small box witha glass cover on it. A magnetisedneedle is pivoted inside the box,which can rotate freely (Fig. 13.10).

In which direction is the maingate of your school situatedfrom your classroom?

Fig. 13.10 A compass

131FUN WITH MAGNETS

The compass also has a dial withdirections marked on it. The compassis kept at the place where we wish toknow the directions. Its needleindicates the north-south directionwhen it comes to rest. The compassis then rotated until the north andsouth marked on the dial are at thetwo ends of the needle. To identifythe north-pole of the magneticneedle, it is usually painted in adifferent colour.

13.4 MAKE YOUR OWN MAGNET

There are several methods of makingmagnets. Let us learn the simplestone. Take a rectangular piece of iron.Place it on the table. Now take a barmagnet and place one of its polesnear one edge of the bar of iron.Without lifting the bar magnet, moveit along the length of the iron bar tillyou reach the other end. Now, lift themagnet and bring the pole (the samepole you started with) to the samepoint of the iron bar from which youbegan (Fig. 13.11). Move the magnetagain along the iron bar in the samedirection as you did before. Repeatthis process about 30-40 times.Bring a pin or some iron filings nearthe iron bar to check whether it hasbecome a magnet. If not, continuethe process for some more time.

Remember that the pole of themagnet and the direction of itsmovement should not change. Youcan also use an iron nail, a needleor a blade and convert them into amagnet.

You now know how to make amagnet. Would you like to make yourown compass?

Activity 6Magnetise an ironneedle using a barmagnet. Now,insert themagnetised needlethrough a smallpiece of cork orfoam. Let the corkfloat in water in abowl or a tub.Make sure thatthe needle doesnot touch the water (Fig. 13.12).Your compass is now ready to work.Make a note of the direction in whichthe needle points when the cork isfloating. Rotate the cork, with theneedle fixed in it, in differentdirections. Note the direction inwhich the needle points when thecork begins to float again withoutrotating. Does the needle alwayspoint in the same direction, whenthe cork stops rotating?

13.5 ATTRACTION AND REPULSION

BETWEEN MAGNETS

Let us play another interesting gamewith magnets. Take two small toy carsand label them A and B. Place a barmagnet on top of each car along itslength and fix them with rubber bandsFig.13.11 Making your own magnet

Fig. 13.12 Acompass in a cup

132 SCIENCE

(Fig. 13.13). In car A, keep the southpole of the magnet towards its front.Place the magnet in opposite directionin car B. Now, place the two cars closeto one another (Fig. 13.13). What doyou observe? Do the cars remain attheir places? Do the cars run awayfrom each other ? Do they movetowards each other and collide?Record your observations in a tableas shown in Table 13.3. Now, placethe toy cars close to each other suchthat the rear side of car A faces thefront side of car B. Do they moveas before? Note the direction in whichthe cars move now. Next, place thecar A behind car B and note thedirection in which they move in eachcase (Fig 13.14). Repeat the activityby placing cars with their rear sidesfacing each other. Record your

observations in each case.What do we find from this

activity? Do two similar poles attractor repel each other? What aboutopposite poles — do they attract orrepel each other?

This property of the magnets canalso be observed by suspending amagnet and bringing one by one thepoles of another magnet near it.

Fig. 13.13 Do opposite poles attract eachother?

Fig. 13.14 Repulsion between similarpoles?

Table 13.3

sracehtfonoitisoP

ehtodwoH?evomsrac

/sdrawotevoMmorfyawa

/rehtohcaellataevomton

gnicafAracfotnorFBracfotnorfeht

gnicafAracforaeRBracfotnorfeht

dnihebdecalpAraCBrac

gnicafBracforaeRAracforaer

Boojho has this question foryou. What will happen if amagnet is broughtnear a compass?

A Few CautionsMagnets loose their properties if theyare heated, hammered or droppedfrom some height (Fig. 13.15). Also,magnets become weak if they are not

Fig. 13.15 Magnets lose their property onheating, hammering and droping

133FUN WITH MAGNETS

Fig. 13.16 Store your magnets safely

ssapmoC

tengaM

etitengaM

elophtroN

elophtuoS

Magnetite is a natural magnet.

Magnet attracts materials like iron, nickel, cobalt. These are called magneticmaterials.

Materials that are not attracted towards magnet are called non-magnetic.

Each magnet has two magnetic poles—North and South.

A freely suspended magnet always aligns in N-S direction.

Opposite poles of two magnets attract each other whereas similar poles repelone another.

stored properly. To keep them safe,bar magnets should be kept in pairswith their unlike poles on the sameside. They must be separated by apiece of wood while two pieces of softiron should be placed across theirends (Fig. 13.16). For horse-shoe

magnet, one should keep a piece ofiron across the poles.

Keep magnets away fromcassettes, mobiles, television, musicsystem, compact disks (CDs) and thecomputer.

Summary

Key Words

134 SCIENCE

1. Fill in the blanks in the following

(i) Artificial magnets are made in different shapes such as __________,__________ and ____________.

(ii) The Materials which are attracted towards a magnet are called________.

(iii) Paper is not a ______ material.

(iv) In olden days, sailors used to find direction by suspending a piece of___________.

(v) A magnet always has __________ poles.

2. State whether the following statements are true or false

(i) A cylindrical magnet has only one pole.

(ii) Artificial magnets were discovered in Greece.

(iii) Similar poles of a magnet repel each other.

(iv) Maximum iron filings stick in the middle of a bar magnet when it is broughtnear them.

(v) Bar magnets always point towards North-South direction.

(vi) A compass can be used to find East-West direction at any place.

(vii) Rubber is a magnetic material.

3. It was observed that a pencil sharpener gets attracted by both the poles of amagnet although its body is made of plastic. Name a material that might havebeen used to make some part of it.

4. Column I shows different positions in which one pole of a magnet is placednear that of the other. Column II indicates the resulting action between themfor each situation. Fill in the blanks.

InmuloC IInmuloC

N-N _________

_________-N noitcarttA

N-S _________

S-_________ noitslupeR

5. Write any two properties of a magnet.

6. Where are poles of a bar magnet located?

7. A bar magnet has no markings to indicate its poles. How would you find outnear which end is its north pole located?

8. You are given an iron strip. How will you make it into a magnet?

9. How is a compass used to find directions?

10. A magnet was brought from different directions towards a toy boat that has

Exercises

135FUN WITH MAGNETS

SOME SUGGESTED ACTIVITIES

1. Using a compass, find the direction in which windows and entrance to yourhouse or class room open.

2. Try to place two equal sized bar magnets one above the other such thattheir north poles are on the same side. Note what happens and write yourobservations in your note book.

3. Few iron nails and screws got mixed with the wooden shavings while acarpenter was working with them. How can you help him in getting thenails and screws back from the scrap without wasting his time in searchingwith his hands?

4. You can make an intelligent doll, which picks up the things it likes (Fig.13.17). Take a doll and attach a small magnet in one of its hands. Coverthis hand with small gloves so that the magnet is not visible. Now, yourintelligent doll is ready. Ask your friends to bring different objects near thedoll's hand. Knowing the material of the object you can tell in advancewhether the doll would catch it or not.

been floating in water in a tub. Affect observed in each case is stated inColumn I. Possible reasons for the observed affects are mentioned inColumn II. Match the statements given in Column I with those in Column II.

InmuloC IInmuloC

tengamehtsdrawotdetcarttastegtaoB htronhtiwtengamahtiwdettifsitaoBdaehstisdrawotelop

tengamehtybdetceffatonsitaoB htuoshtiwtengamahtiwdettifsitaoBdaehstisdrawotelop

htronfitengamehtsdrawotsevomtaoBstiraenthguorbsitengamehtfoelop

daeh

stignoladexiftengamllamsasahtaoBhtgnel

nehwtengamehtmorfyawasevomtaoBdaehstiraenthguorbsielophtron lairetamcitengamfoedamsitaoB

noitceridstignignahctuohtiwstaolftaoB lairetamcitengam-nonpuedamsitaoB

Fig. 13.17 An intelligent dollTHINGS TO READ

Gulliver's Travels which has this fantasy of the whole island of Laputa, float-ing in air. Could magnets be involved?

Water14Suppose for some reason your

family gets only one bucket ofwater everyday for a week.

Imagine what would happen? Wouldyou be able to cook, clean utensils,wash clothes or bath? What are theother activities you would not be ableto do? What would happen if we donot have easy access to water for along period of time?

Apart from drinking, there areso many activities for which we usewater (Fig. 14.1). Do you have anidea about the quantity of water weuse in a single day?

14.1 HOW MUCH WATER DO WE

USE?

Activity 1

List all the activities for which youuse water in a day. Some activitiesare listed in Table 14.1. Make a

similar table in your notebook.Throughout the day, measure theamount of water used for eachactivity by you and other familymembers. You may use a mug, aglass, a bucket or any other containerto measure the amount of water used.

Table 14.1 Estimation of theamount of water used by a

family in a day

ytivitcA fotnuomAdesuretaw

gniknirD

gnihsurB

gnihtaB

slisnetugnihsaW

sehtolcgnihsaW

stelioT

roolfgninaelC

rehtoynA

nidesuretawlatoTylimafaybyada

You now have a rough idea as tohow much water your family uses ina day. Using this information,calculate the amount of waterneeded by your family in a year. Now,divide this amount by the number

Fig. 14.1 Uses of water

137WATER

of members of your family. This willgive an idea of the amount of waterneeded by one member of your familyin a year. Find the number of peoplethat live in your village or town. Youmay now get an idea of the amountof water needed by your village ortown in a year.

You have listed a number ofactivities for which you use water. Doyou think, our water requirement islimited to activities like these? We usewheat, rice, pulses, vegetables andmany other food items everyday. Weknow that some of the fibres that weuse for making fabric come fromplants. Is water not needed to growthese? Can you think of some moreuses of water? Water is used inindustries for producing almost allthe things that we use. So, we needwater not only for our daily activitiesbut also for producing many things.

14.2 WHERE DO WE GET WATER

FROM?Where do you get the water that youuse? Some of you may say, “We drawwater from a river, spring, pond, wellor a hand pump”. Some others mightsay, “We get water from taps”. Haveyou ever wondered where water inthe taps comes from? Water that weget from taps is also drawn from alake or a river or a well (Fig. 14.2). Itis then supplied through a networkof pipes.

Each of us may be getting waterinto our homes in different ways.But, finally, all of us get water fromthe same sources such as ponds,lakes, rivers and wells.

We have discussed some of thesources of water. Where does thewater come from, to fill these ponds,lakes, rivers and wells?

Do you know that about twothirds of the Earth is covered withwater? Most of this water is in oceansand seas (Fig. 14.3).

Boojho wonders whetherpeople living in dif ferentregions of our country get thesame amount of water. Arethere regions where people donot get adequate amount ofwater? How do theymanage?

Fig. 14.2 Water in taps comes from rivers,lakes or wells

Paheli wants to tell you thatabout two glasses ofwater are required toproduce each page of abook.

138 SCIENCE

The water in the oceans and seashas many salts dissolved in it — thewater is saline. So, it is not fit fordrinking and other domestic,agricultural and industrial needs.You might have heard the famouslines of the poem “Rime of the AncientMariner” written by S.T. Coleridge in1798:

“Water water every where

Nor any drop to drink”

Here the poet has described theplight of sailors on a ship lost in theocean.

Yet, oceans play an important rolein supplying the water that we use.Do you find this surprising? After all,the water that we use is not salty.Many of us live in places far awayfrom the oceans. Does the watersupply in these places also dependon the oceans? How does the oceanwater reach ponds, lakes, rivers andwells, which supply us water? Howcome the water from these sourcesis not saline anymore?

That is where the water cyclecomes in!

14.3 WATER CYCLE

Disappearing Trick of WaterHow many times have you noticedthat water spilled on a floor dries upafter some time? The water seems todisappear. Similarly, water disappearsfrom wet clothes as they dry up(Fig. 14.4). Water from wet roads,rooftops and a few other places alsodisappears after the rains. Where doesthis water go?

Boojho wants you to imaginea day in your life when watersupply through taps is notavailable. So, you have tofetch it yourself from afar away place. Wouldyou use the sameamount of water as onany other day?

Fig. 14.3 Oceans cover a major part of theearth

Fig. 14.4 Clothes drying on a clothes-line

Do you remember Activity 6 inChapter 5 in which water with saltdissolved in it was heated? What did

139WATER

we find? The water evaporated andthe salt was left behind. This activitygives us an idea that, on heating,water changes into its vapour. Wealso realise from this activity, thatwater vapour does not carry away thesalt with it. Water vapours so formedbecome a part of the air and cannotusually be seen. We also found thatheating is essential to convert waterinto its vapour. However, we haveseen that water changes into itsvapour also from the fields, roads,rooftops and other land areas. We alsodiscussed in Chapter 5 that to obtainsalt, water from the sea is left inshallow pits to let the water evaporate.From where does this water get theheat it needs to evaporate? Let us findout.

Activity 2

Take two similar plates. Place one ofthe plates in sunlight and keep theother under shade. Now, pour equalamount of water in each of the plates(Fig. 14.5). You can use a cap of abottle to measure water. Make surethat water does not spill over.Observe the two plates after every 15minutes. Does the water seem todisappear? From which plate does itdisappear first? What is the sourceof heat for this evaporation?

During the daytime, sunlight fallson the water in oceans, rivers, lakesand ponds. The fields and other landareas also receive sunlight. As aresult, water from all these placescontinuously changes into vapour.However, the salts dissolved in thewater are left behind.

In Activity 2, did you find thatwater also disappeared from the plate

Fig.14.5 Evaporation of water in sunlightand in shade

kept in the shade, though it couldhave taken more time? Does the heatfrom the sunlight reach here? Yes,during the daytime all the airsurrounding us gets heated. Thiswarm air provides heat forevaporation of water in the shade.Thus, evaporation takes place fromall open surfaces of water. As a result,water vapour gets continuouslyadded to air. However, evaporation ofwater is a slow process. That is whywe rarely notice its loss from a bucketfull of water. In sunlight, evaporationtakes place faster. On heating wateron a burner, its evaporation takesplace even faster. Is there any otherprocess through which water vapourgets transferred into air?

Loss of Water by PlantsYou have learnt in Chapter 7 thatplants need water to grow. Plants usea part of this water to prepare theirfood and retain some of it in theirdifferent parts. Remaining part of

140 SCIENCE

this water is released bythe plants into air, aswater vapour through the process oftranspiration. Do you rememberobserving transpiration of water byplants in Activity 4 in Chapter 7?

Water vapour enters the air throughthe processes of evaporation andtranspiration. Is it lost for ever? No, weget it back again, as we will see.How are clouds formed?

Activity 3Take a glass half filled with water.Wipe the glass from the outside witha clean piece of cloth. Add some iceinto the water. Wait for one or twominutes. Observe the changes thattake place on the outer surface of theglass (Fig.14.6).

From where do water drops appearon the outer side of the glass? The coldsurface of the glass containing icedwater, cools the air around it, and thewater vapour of the air condenses onthe surface of the glass. We noticedthis process of condensation in Activity7 in Chapter 5.

The process of condensation playsan important role in bringing waterback to the surface of earth. Howdoes it happen? As we go higher fromthe surface of the earth, it gets cooler.When the air moves up, it gets coolerand cooler. At sufficient heights, theair becomes so cool that the watervapour present in it condenses toform tiny drops of water calleddroplets. It is these tiny droplets thatremain floating in air and appear tous as clouds (Fig. 14.7).

It so happens that many dropletsof water come together to form larger

Fig. 14.6 Drops of water appear on outersurface of the glass containing water with ice

Boojho has been reading abouttranspiration. He askedhimself-how much water islost through transpiration bywheat plants that give us onekilogram of wheat? He foundout that this is nearly 500litres, that is, roughly 25 largesized buckets full of water. Canyou now imagine the amountof water lost by plants of all theforests, crops and grasslandstogether?

Paheli has noticed dew on leavesof grass on winter mornings. Didyou notice something similar onleaves or metal surfaces likeiron grills and gates on a coldmorning? Is this also due tocondensation? Do you seethis happening on hotsummer mornings?

141WATER

Snow in the mountains melts intowater. This water flows down themountains in the form of streamsand rivers (Fig. 14.8). Some of thewater that falls on land as rain, alsoflows in the form of rivers andstreams. Most of the rivers cover longdistances on land and ultimately fallinto a sea or an ocean. However, waterof some rivers flows into lakes.

Fig. 14.7 Clouds

Boojho has noticed fog near theground in winter mornings. Hewonders if this is alsocondensation ofwater vapour nearthe ground. What doyou think?

sized drops of water. Some drops ofwater become so heavy that theybegin to fall. These falling water-drops are, what we call rain. Inspecial conditions, it may also fall ashail or snow.

Thus, water in the form of vapourgoes into air by evaporation andtranspiration, forms clouds, andthen comes back to the ground asrain, hail or snow.

14.4 BACK TO THE OCEANS

What happens to the water that rainand snow bring to different regions ofearth? Almost all land surfaces areabove the level of oceans. Most of thewater that falls on the land as rain andsnow sooner or later goes back to theoceans. This happens in many ways.

Fig. 14.8 Rain water flows down in the formof streams and rivers

The rainwater also fills up thelakes and ponds. A part of therainwater gets absorbed by theground and seems to disappear inthe soil. Some of this water isbrought back to the air by the processof evaporation and transpiration. Therest seeps into the ground. Most ofthis water becomes available to usas ground water. Open wells are fedby ground water. Ground water is thesource for many lakes as well. It isalso this ground water which isdrawn by a handpump or a tubewell.The more handpumps or tubewellsthat are used in an area, the deeperwe need to dig to find this groundwater. The loss in the level of groundwater due to over use, is worrisome.

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Paheli wants to share a concernwith you. In those areas where theland has little or no vegetation, therainwater flows away quickly. Flowingrainwater also takes the top layer ofthe soil away with it. There are fewareas where most of the land iscovered with concrete. This reducesthe seepage of rainwater into theground which ultimately affects theavailability of ground water.

We now know that water broughtback to the surface of the earth byrain, hail or snow, goes back tooceans. Thus, water from the oceanand surface of the earth goes intoair as vapour, returns as rain, hailor snow and finally goes back to theoceans. The circulation of water inthis manner is known as the watercycle (Fig.14.9). This circulation ofwater between ocean and land is acontinuous process. This maintainsthe supply of water on land.

14.5 WHAT IF IT RAINS HEAVILY?The time, duration and the amountof rainfall varies from place to place.In some parts of the world it rains

Fig. 14.9 Water cycle

Fig. 14.10 A scene after heavy rains

throughout the year while there areplaces where it rains only for a fewdays. In our country, most of therainfall occurs during the monsoonseason. Rains bring relief especially

143WATER

after hot summer days. The sowingof many crops depends on the arrivalof monsoon.

However, excess of rainfall maylead to many problems (Fig. 14.10).

lose water by evaporation andtranspiration. Since it is not beingbrought back by rain, the soilbecomes dry. The level of water inponds and wells of the region goesdown and some of them may evendry up. The ground water may alsobecome scarce. This may lead todrought.

In drought conditions, it isdifficult to get food and fodder. Youmight have heard about droughtsoccurring in some parts of ourcountry or the world. Are you awareof the difficulties faced by the peopleliving in these areas? What happensto the animals and the vegetation inthese conditions? Try and find outabout this by talking to your parentsand neighbours and by readingabout it from newspapers andmagazines.

14.7 HOW CAN WE CONSERVE WATER?Only a small fraction of wateravailable on the Earth is fit for useof plants, animals and humans. Mostof the water is in the oceans and itcannot be used directly. When thelevel of the ground water decreasesdrastically, this can not be used anymore. The total amount of water onEarth remains the same, but, thewater available for use is very limitedand is decreasing with over usage.

The demand for water isincreasing day-by-day. The numberof people using water is increasingwith rising population. In many

Fig. 14.11 A scene of a flooded area

Heavy rains may lead to rise in thelevel of water in rivers, lakes andponds. The water may then spreadover large areas causing floods. Thecrop fields, forests, villages, and citiesmay get submerged by water(Fig. 14.11). In our country, floodscause extensive damage to crops,domestic animals, property andhuman life.

During floods, the animals livingin the water also get carried awaywith the water. They often get trappedon land areas and die whenfloodwater recedes. Rains also affectthe animals living in the soil.

14.6 WHAT HAPPENS IF IT DOES

NOT RAIN FOR A LONG

PERIOD?Can you imagine what would happenif it does not rain in a region for ayear or more? The soil continues to

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cities, long queues for collection ofwater are a common site (Fig. 14.12).Also, more and more water is beingused for producing food and by theindustries. These factors are leadingto shortage of water in many partsof the world. Hence, it is veryimportant that water is usedcarefully. We should take care not towaste water.

14.8 RAINWATER HARVESTING

One way of increasing the availabilityof water is to collect rainwater andstore it for later use. Collectingrainwater in this way is calledrainwater harvesting. The basicidea behind rainwater harvesting is“Catch water where it falls”.

What happens to the rainwaterthat falls in places that are mostlycovered with concrete roads andbuildings? It flows into the drains,isn't it? From there water goes torivers or lakes, which could be far

Fig. 14.12 A queue for collecting water

Fig. 14.13 Rooftop rainwater harvesting

away. A lot of effort will then berequired to get this water back intoour homes as the water did not seepinto the ground.

Discussed here are two techniq-ues of rainwater harvesting:1. Rooftop rainwater harvesting: In

this system the rainwater iscollected from the rooftop to astorage tank, through pipes. Thiswater may contain soil from theroof and need filtering before it isused. Instead of collectingrainwater in the tank, the pipescan go directly into a pit in theground. This then seeps into thesoil to recharge or refill the groundwater (Fig. 14.13).

2. Another option is to allow waterto go into the ground directlyfrom the roadside drains thatcollect rainwater.

145WATER

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1. Fill up the blanks in the following:

(a) The process of changing of water into its vapour is called _________________.

(b) The process of changing water vapour into water is called _________________.

(c) No rainfall for a year or more may lead to _________________ in that region.

(d) Excessive rains may cause _________________.

2. State for each of the following whether it is due to evaporation or condensation:

(a) Water drops appear on the outer surface of a glass containing cold water.

(b) Steam rising from wet clothes while they are ironed.

Water is essential for life.

Water vapour gets added to air by evaporation and transpiration.

The water vapour in the air condenses to form tiny droplets of water,which appear as clouds. Many tiny water droplets come together and falldown as rain, snow or hail.

Rain, hail and snow replenish water in rivers, lakes, ponds, wells andsoil.

The circulation of water between ocean and land is known as thewater cycle.

Excessive rains may cause floods while lack of it for long periods maycause droughts.

The amount of usable water on earth is limited so it needs to be usedcarefully.

Summary

Key Words

Exercises

146 SCIENCE

(c) Fog appearing on a cold winter morning.

(d) Blackboard dries up after wiping it.

(e) Steam rising from a hot girdle when water is sprinkled on it.

3. Which of the following statements are “true” ?

(a) Water vapour is present in air only during the monsoon. ( )

(b) Water evaporates into air from oceans, rivers and lakes but not from the soil.( )

(c) The process of water changing into its vapour, is called evaporation.( )

(d) The evaporation of water takes place only in sunlight.( )

(e) Water vapour condenses to form tiny droplets of water in the upper layers of airwhere it is cooler.( )

4. Suppose you want to dry your school uniform quickly. Would spreading it near ananghiti or heater help? If yes, how?

5. Take out a cooled bottle of water from refrigerator and keep it on a table. After sometime you notice a puddle of water around it. Why?

6. To clean their spectacles, people often breathe out on glasses to make them wet.Explain why the glasses become wet.

7. How are clouds formed?

8. When does a drought occur?


1. List three activities in which you can save water. For each activity describehow you would do it.

2. Collect pictures relating to floods or droughts from old magazines ornewspapers. Paste them in your notebook and write about the problemsthat people would have faced.

3. Prepare a poster on ways of saving water and display it on your schoolnotice board.

4. Write a few slogans of your own on the topic ‘Save Water’.

Air Around us15We have learnt in Chapter 9

that all living things requireair. But, have you ever seen

air? You might not have seen air, but,surely you must have felt its presencein so many ways. You notice it whenthe leaves of the trees rustle or theclothes hanging on a clothes-linesway. Pages of an open book beginfluttering when the fan is switchedon. The moving air makes it possiblefor you to fly your kite. Do youremember Activity 3 in Chapter 5 inwhich you separated the sand andsawdust by winnowing? Winnowingis more effective in moving air. Youmay have noticed that during stormsthe wind blows at a very high speed.It may even uproot trees and blowoff the rooftops.

Have you ever played with a firki(Fig. 15.1)?

Hold the stick of the firki and placeit in different directions in an openarea. Move it a little, back and forth.Observe, what happens. Does thefirki rotate? What makes a firki rotate— moving air, isn’t it?

Have you seen a weather cock(Fig. 15.3)? It shows the direction inwhich the air is moving at that place.

Fig. 15.1 Different types of firki

Fig. 15.2 Making a simple firki

Fig. 15.3 A weather cock

Activity 1

Let us make a firki of our own,following the instructions shown inFig. 15.2.

15.1 IS AIR PRESENT

EVERYWHERE AROUND US?Close your fist — what do you havein it? Nothing? Try the followingactivity to find out.

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Activity 2

Take an empty glass bottle. Is it reallyempty or does it have somethinginside? Turn it, upside down. Issomething inside it, now?

Now, dip the open mouth of thebottle into the bucket filled with wateras shown in Fig. 15.4. Observe thebottle. Does water enter the bottle?Now tilt the bottle slightly. Does thewater now enter the bottle? Do yousee bubbles coming out of the bottleor hear any bubbly sound? Can younow guess what was in the bottle?

Yes! You are right. It is “air”, thatwas present in the bottle. The bottlewas not empty at all. In fact, it wasfilled completely with air even whenyou turned it upside down. That iswhy you notice that water does notenter the bottle when it is in aninverted position, as there was nospace for air to escape. When thebottle was tilted, the air was able tocome out in the form of bubbles, andwater filled up the empty space thatthe air has occupied.

This activity shows that airoccupies space. It fills all the spacein the bottle. It is present everywherearound us. Air has no colour and onecan see through it. It is transparent.

Our earth is surrounded by a thin

Fig. 15.4 Experiments with an empty bottle.

Fig. 15.5 Mountaineers carry oxygencylinders with them

layer of air. This layer extends up tomany kilometres above the surfaceof the earth and is called atmosphere.

Why do you think, mountaineerscarry oxygen cylinders with them,while climbing high mountains(Fig. 15.5) ?

15.2 WHAT IS AIR MADE UP OF?Until the eighteenth century, peoplethought that air was just onesubstance. Experiments have provedthat it is really not so. Air is amixture of many gases. What kindof a mixture is it? Let us find outabout some of the major componentsof this mixture, one by one.

Water vapourWe have learnt earlier that aircontains water vapour. We also sawthat, when air comes in contact witha cool surface, it condenses anddrops of water appear on the cooledsurfaces. The presence of watervapour in air is important for thewater cycle in nature.

149AIR AROUND US

Oxygen

Activity 3In the presence of your teacher, fix twosmall candles of the same size in themiddle of two shallow containers. Now,fill the containers with some water.Light the candles and then cover each

NitrogenIn Activity 3 did you observe that amajor part of air is still present inthe glass bottle even after the candleblew out? This indicates the presenceof some component in the air, whichdoes not support burning. The majorpart of air (which does not supportburning candle) is nitrogen. It takesup nearly four-fifth of the space thatair fills.

Carbon dioxideIn a closed room, if there is somematerial that is burning, you mayhave felt suffocation. This is due toexcess of carbon dioxide that may beaccumulating in the room, as theburning continues. Carbon dioxidemakes up a small component of theair around us. Plants and animalsconsume oxygen for respiration andproduce carbon dioxide. Plant andanimal matter on burning, alsoconsumes oxygen and producesmainly carbon dioxide and a fewother gases.

Dust and smokeThe burning of fuel also producessmoke. Smoke contains a few gasesand fine dust particles and is oftenharmful. That is why you see longchimneys in factories. This takes theharmful smoke and gases away fromour noses, but, brings it closer to thebirds flying up in the sky!

Dust particles are always presentin air.

Activity 4Find a sunny room in your school/home. Close all the doors andwindows with curtains pulled downto make the room dark. Now, open

Fig. 15.6 Air has oxygen

one of them with an inverted glass (onemuch taller than the other) as shownin Fig. 15.6. Observe carefully whathappens to the burning candles andthe water level.

Do the candles continue to burnor go off? Does the level of water insideglasses remain the same?

The burning of the candle mustbe due to presence of some componentof air, isn’t it? Do you find anydifference in your observation with thetwo glasses of different heights? Whatcan be the reason for this?

Burning can occur only in thepresence of oxygen. We see that, onecomponent of air is oxygen. Now, theamount of air and hence its oxygencomponent inside each glass in ourexperiment, is limited. When most ofthis oxygen is used up by the burningcandle, it can no longer burn andblows out. Also, some of the spaceoccupied by the oxygen inside theglass becomes empty and the waterrises up to fill or occupy this space.

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the door or a window facing the sun,just a little, in such a way that itallows sunlight to enter the roomonly through a slit. Look carefullyat the incoming beam of sunlight.

Do you see some tiny shiningparticles moving in the beam ofsunlight (Fig. 15.7)? What are theseparticles?

During cold winters you mighthave observed similar beam ofsunlight filter through the trees inwhich dust particles appear to dancemerrily around!

This shows that air also containsdust particles. The presence of dustparticles in air varies from time totime, and from place to place.

We inhale air when we breathethrough our nostrils. Fine hair andmucus are present inside the noseto prevent dust particles from gettinginto the respiratory system.

Do you recall being scolded byyour parents when you breathethrough your mouth? If you do that,harmful dust particles may enteryour body.

We may conclude, then, that aircontains some gases, water vapourand dust particles. The gases in airare mainly nitrogen, oxygen, smallamount of carbon dioxide, and manyother gases. However, there may besome variations in the compositionof air from place to place. We see thatair contains mostly nitrogen and

Fig. 15.7 Observing presence of dust in airwith sunlight

Boojho is asking you,why do you think, thepoliceman in Fig. 15.8 iswearing a mask?

Fig.15.8 Policemen regulating traffic at acrowded crossing often wear amask

Paheli wants to know,why the transparentglass of windows, if notwiped off regularly,appears hazy?

Boojho wants to know,why during an inci-dent of fire, one isadvised to wrap awoollen blanket over aburning object.

151AIR AROUND US

oxygen. In fact, these two gasestogether make up 99% of the air. Theremaining 1% is constituted bycarbon dioxide and a few other gases,water vapour and dust particles(Fig. 15.9).

15.3 HOW DOES OXYGEN BECOME

AVAILABLE TO ANIMALS AND PLANTS

LIVING IN WATER AND SOIL?

Activity 5

Take some water in a glass vessel orbeaker. Heat it slowly on a tripodstand. Well before the water beginsto boil, look carefully at the inner

surface of the vessel. Do you see tinybubbles on the inside (Fig. 15.10)?

These bubbles come from the airdissolved in water. When you heatthe water, to begin with, the airdissolved in it escapes. As youcontinue heating, the water itselfturns into vapour and finally beginsto boil. We learnt in Chapters 8 and9, that the animals living in wateruse the dissolved oxygen in water.

The organisms that live in soilalso need oxygen to respire, isn’t it?How do they get the air they need,for respiration?

Activity 6

Take a lump of dry soil in a beakeror a glass. Add water to it and notewhat happens (Fig. 15.11). Do yousee bubbles coming out from soil?These bubbles indicate the presenceof air in the soil.

When the water is poured on thelump of soil, it displaces the air whichis seen in the form of bubbles. Theorganisms that live inside the soiland the plant roots respire in this

Nitro-gen

oxygen

carbon dioxide,water vapourand other gases

Fig.15.9 Composition of air

Fig. 15.10 Water contains air!

Here is a question from Paheli,“Will the tiny air bubbles seenbefore the water actually boils,also appear if we do thisactivity by reheating boiledwater kept in an air tightbottle?” If you do notknow the answer youmay try doing it andsee for yourself.

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air. A lot of burrows and holes areformed in deep soil by the animalsliving in the soil. These burrows alsomake spaces available for air to movein and out of the soil. However, whenit rains heavily, water fills up all thespaces occupied by the air in the soil.In this situation, animals living inthe soil have to come out forrespiration. Could this be the reasonwhy earthworms come out of the soil,only during heavy rains?

Have you ever wondered why allthe oxygen of atmosphere does notget used up though a large numberof organisms are consuming it? Whois refilling the oxygen in theatmosphere?

15.4 HOW IS THE OXYGEN IN THEATMOSPHERE REPLACED?

In Chapter 7, we read aboutphotosynthesis. In this process,plants make their own food andoxygen is produced along with it.Plants also consume oxygen forrespiration, but they produce moreof it than they consume. That is whywe say plants produce oxygen.

It is obvious that animals cannotlive without plants. Similarly, plants

can not survive for long withoutanimals. They would consume all thecarbon dioxide in the atmosphere.We can see that both need each other,as the balance of oxygen and carbondioxide in the atmosphere is thusmaintained. This shows theinterdependence of plants andanimals.

We can now appreciate, howimportant air is for life on earth. Arethere any other uses of air? Have youheard about a windmill? Look atFig. 15.12.

Fig. 15.11 Soil has air in it

Fig. 15.12 A windmill

The wind makes the windmillrotate. The windmill is used todraw water from tubewells and torun flour mills. Windmills are alsoused to generate electricity. Airhelps in the movements of sailingyachts, gliders, parachutes andaeroplanes. Birds, bats and insectscan fly due to the presence of air.Air also helps in the dispersal ofseeds and pollen of flowers ofseveral plants. Air plays animportant role in water cycle.

153AIR AROUND US

Air is found everywhere. We cannot see air, but we can feel it.

Air in motion is called wind.

Air occupies space.

Air is present in water and soil.

Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour and afew other gases. Some dust particles may also be present in it.

Oxygen supports burning and is necessary for living organisms.

The envelope of air that surrounds the earth is known as atmosphere.

Atmosphere is essential for life on earth.

Aquatic animals use dissolved air in water for respiration.

Plants and animals depend on each other for exchange of oxygen andcarbon dioxide from air.

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1. What is the composition of air?

2. Which gas in the atmosphere is essential for respiration?

3. How will you prove that air supports burning?

4. How will you show that air is dissolved in water?

5. Why does a lump of cotton wool shrink in water?

Summary

Exercises

Key Words

154 SCIENCE


1. On a clear glass window facing towards an open area, fix a small rectangu-lar strip of paper. Remove the strip after a few days. Do you notice a differ-ence between the rectangular section that was left covered with paper andthe rest of the glass window? By repeating this exercise every month, youcan have an idea about the amount of dust present in air around you atdifferent times of the year.

2. Observe the leaves of trees, shrubs or bushes planted by the roadside. Notewhether their leaves have some dust or soot deposited over them. Takesimilar observations with the leaves of trees in the school compound or in agarden. Is there any difference in deposition of soot on leaves of trees nearthe roadside? What could be the possible reasons for this difference? Takea map of your city or town and try to identify regions in the map where youhave noticed very thick layer of soot on the plants by the roadside. Com-pare with results obtained by other classmates and mark these areas onthe map. Perhaps the results from all the students could be summarisedand reported in newspapers.

6. The layer of air around the earth is known as ___________.

7. The component of air used by green plants to make their food, is ___________.

8. List five activities that are possible due to the presence of air.

9. How do plants and animals help each other in the exchange of gases in theatmosphere?

Garbage in, Garbage out16We throw out so much rubbish

or garbage everyday fromour homes, schools, shops

and offices. The grains, pulses,biscuits, milk or oil purchased inshops, are packed in plastic bags ortins. All these wrapping material goout as garbage. We sometimes buythings that are rarely used and oftenthrown into the garbage.

We generate so much garbage inour day-to-day activities! We oftenthrow groundnut shells on publicplaces, in buses or trains, after eatingthe nuts. We throw away the ticketwhen we get off a bus. A child mightgo on sharpening pencils just forfun. If we make mistakes or spill inkon our notebook, we tear off the sheetand throw it away. And we also throwaway many domestic wastes such asbroken toys, old clothes, shoes andslippers.

What if the garbage is not removedfrom our homes and surroundings?How do you think, this will harm us?When safai karamcharis take thegarbage from the bins, where doesthe garbage go and what happens toit? Is it possible for all of this garbageto be changed into something thatwill not harm us? Can we contributetowards this in any way? We will lookfor answers to these questions, in thischapter.

Children from Paheli and Boojho’sschool did a project called ‘Dealingwith Garbage’. We will learn aboutsome of the things they learntthrough this project.

16.1 DEALING WITH GARBAGE

Safai karamcharis collect the garbagein trucks and take it to a low lyingopen area, called a landfill (Fig. 16.1).

There the part of the garbage thatcan be reused is separated out fromthe one that cannot be used as such.Thus, the garbage has both usefuland non-useful components. The

Fig. 16.1 A landfill

156 SCIENCE

non-useful component is separatedout. It is then spread over the landfilland then covered with a layer of soil.Once the landfill is completely full,it is usually converted into a park ora play ground. For the next 20 yearsor so, no building is constructed onit. To deal with some of the usefulcomponents of garbage, compostmaking areas are developed near thelandfill. What is compost? Let uslearn about it, from the followingactivity.

Activity 1

Collect the garbage from your housebefore it is thrown into the dustbin.Separate it into two groups, so thatthey have:

Group 1: Garbage from thekitchen — like fruit and vegetablepeels, egg shells, waste food, tealeaves. Include newspapers, dryleaves and paper bags in this group.

Group 2: Pieces of cloth,polythene bags, broken glass,aluminium wrappers, nails, oldshoes and broken toys.

Now divide the contents of eachgroup into two separate heaps. Label

them as A, B, C and D. Put one heapfrom Group 1 and one heap fromGroup 2 into two separate plasticbags. Tie the mouth of these twobags tightly. Put all the four heapsin separate pits and cover them withsoil (Fig. 16.2). You can also use fourpots to bury these garbage heaps.

Remove the soil after four daysand observe the changes in thegarbage. A black colour and no foulsmell indicates that rotting ofgarbage is complete. Put the heapsagain in the pits and cover with thesoil. Observe again after every twodays and note your observations assuggested. Did the garbage.(i) rot completely and not smell?(ii) rot only partially?(iii) rot almost completely, but still

smells bad?(iv) not change at all?

Garbage in which heap was seento rot and which did not?

Enter options (i), (ii), (iii) or (iv) inthe columns of Table 16.1 based onyour observations. If you make any

Paheli did wonder as to whatcould be useful garbage? Whywas it thrown away in the firstplace? Is there some garbagethat is not actuallygarbage?

Fig. 16.2 Putting garbage heaps in pits

157GARBAGE IN, GARBAGE OUT

noticed that this type ofwastes rot completelywhen buried in the soil.Do you see why it isnecessary for us toseparate waste into twogroups as we did inActivity 1, before wethrow it?

Have you noticedgarbage heaps of driedleaves on the roadside?Most of the time these

are burnt (Fig. 16.3). Farmers toooften burn the husk, dried leaves andpart of crop plants in their fields afterharvesting. Burning of these,produces smoke and gases that areharmful to our health. We should tryto stop such practices. These wastescould be converted into usefulcompost.

Table 16.1 What has happened tothe garbage heaps?

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other observations, do not forget towrite all these down in yournotebook. Do not remove and burnthe garbage that did not rot.

If the garbage was found to rotcompletely and did not smell, mix itin the soil where you sow yourfavourite plants. This would providenutrients to the plants.

You must have observed from thisactivity that some things in thegarbage rot. They form manurewhich is used for the plants. Therotting and conversion of somematerials into manure is called‘composting’.

In some cities and townsmuncipalities provide separatedustbins for collecting two kinds ofgarbage. Usually one is coloured blueand the other green. The blue bin isfor materials that can be used again —such as plastics, metals and glass.Did you notice that these are thematerials that do not rot in thegarbage heaps? The green bins arefor collecting kitchen and other plantor animal wastes. You may have

Fig. 16.3 Burning of leaves produce harmfulgases

Here are some of the observationsand thoughts, noted by Paheli andBoojho, from their project “Dealingwith Garbage”.

158 SCIENCE

Not theft really . She must havemeant “illegal”. She wanted that thegovernment should make a lawagainst the burning of leaves andother plant wastes anywhere in India.

16.2 VERMICOMPOSTING

We can be friends of plants bysupplying them with compost. Wewill also be very good friends toourselves by making compost.

Talking of friends, do you knowthat earthworms are called farmer’sfriend? Let us find out how a type ofearthworm called redworm is usedfor composting. This method ofpreparing compost with the help ofredworms is called vermicomposting.We can try to make manure byvermicomposting at school.

Activity 2

Let us dig a pit (about 30 cm deep)or keep a wooden box at a place,which is neither too hot nor too cold.What about a place which does notget direct sunlight? Let us now makea comfortable home for our redworms

in the pit or the box.Spread a net or chicken mesh at

the bottom of the pit or the box. Youcan also spread 1 or 2 cm thick layerof sand as an alternative. Now, spreadsome vegetable wastes includingpeels of fruits over this layer of sand.

One can also use green leaves,pieces of dried stalks of plants, huskor pieces of newspaper or carboardto spread over the layer of sand.However, shiny or plastic coatedpaper should not be used for thispurpose. Dried animal dung couldalso be used as a spread over sandor wire mesh.

Sprinkle some water to make thislayer wet. Take care not to use excessof water. Do not press the layer ofwaste. Keep this layer loose so thatit has sufficient air and moisture.

Now, your pit is ready to welcome

Boojho noted in hisnotebook: Do not burnleaves! You will not be ableto tolerate the fumes!

Paheli made a note in hernotebook: Why has thegovernment not madeburning of leaves atheft ?

Fig. 16.4 Redworms

the redworms. Buy some redwormsand put them in your pit (Fig. 16.4).Cover them loosely with a gunny bagor an old sheet of cloth or a layer of


grass. Your redworms need food. Youcan give them vegetable and fruitwastes, coffee and tea remains andweeds from the fields or garden(Fig. 16.5). It might be a good idea tobury this food about 2-3 cm insidethe pit. Do not use wastes that maycontain salt, pickles, oil, vinegar,meat and milk preparations as foodfor your redworms. If you put thesethings in the pit, disease-causingsmall organisms start growing in thepit. Once in a few days, gently mixand move the top layers of your pit.

Redworms do not have teeth. Theyhave a structure called ‘gizzard’, whichhelps them in grinding their food.Powdered egg shells or sea shells couldbe mixed with the wastes. This wouldhelp redworms in grinding their food.A redworm can eat food equal to itsown weight, in a day.

Redworms do not survive in veryhot or very cold surroundings. Theyalso need moisture around them.If you take good care of your worms,in a month’s time their number willdouble.

Observe the contents of the pitcarefully after 3-4 weeks. Do you nowsee loose, soil-like material in the pit?Your vermicompost is ready(Fig. 16.6).

Put some wastes as food in onecorner of the pit. Most of the wormswill shift towards this part of the pit,vacating the other part. Remove thecompost from the vacated part anddry it in the sun for a few hours. Yourvermicompost is ready for use!

The part left in the pit has mostof the worms in it. You can use thesefor preparing more compost or sharethem with another user.

Use this excellent vermicompostin your pots, gardens or fields. Is thisnot like getting the ‘best outof waste’? Those of you whohave agricultural fields can tryvermicomposting in large pits. Youcan save a lot of money that is spenton buying expensive chemicalfertilizers and manure from themarket.

Fig. 16.5 Food for redworms

Fig. 16.6 Vermicomposting

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cousin Shyam had made. Files fromold charts, greeting cards decoratedwith flowers made from pencilshavings, mats from old clothes,baskets from used old polythenebags were some of the items Nanuliked. Shyam had even made a diaryfrom invitation cards!

One morning Nanu went lookingfor his grandmother (Nani). He sawthat she was applying a thick pasteon a basket. Nanu asked, “Nani,What are you doing? What is thispaste?”

“This is papier-mâchè, a pastemade of clay and paper in which Ihave also mixed some rice husk”,replied Nani.

“But, why are you putting it onthe basket?”, asked Nanu.

“To make it stronger”, said Naniand added “would you like to learnthis from me?” Nanu was not verykeen and ran outside to play. He wasonly interested in tearing up papersto make planes. In fact he also startedtearing up papers from Shyam’s files!

Shyam collected all the pieces ofpaper Nanu had used, wonderingwhat to do about him! He just didnot listen to anyone!

It was Nanu’s birthday in a fewdays. Shyam planned to inviteNanu’s friends. Nanu took outmoney from his mud pot and wentto the market. He bought some paperhats for his friends. He asked theshopkeeper for a polythene bag tokeep the hats, who gave him a paperbag instead of polythene. Nanu alsobought many other items likebiscuits and toffees. He found itdifficult to carry all of these thingsas no shopkeeper was ready to give

Fig. 16.7 Neighbourhood garbage dump

16.3 THINK AND THROW

How much of garbage do you think,is thrown out by each houseeveryday? You can make an estimateby using a bucket as a measure. Usea 5-10 litre bucket to collect thegarbage from your home for a fewdays. In how many days does thebucket become full? You know thenumber of members in your family.If you find out the population of yourcity or town, can you now estimatethe number of buckets of garbagethat may be generated in a day inyour city or town? We are generatingmountains of garbage everyday, isn’tit (Fig. 16.7)?

Let us read a story about a villagewhere there is less garbage and morewisdom. Nanu studies in Class VI.He is very fond of making paperplanes. His mother is very annoyedwhen he tears off sheets from newnotebooks to make aeroplanes, butNanu does not care.

Once Nanu went to his aunt’svillage, along with his mother. He wasamazed at the variety of things his


a polythene bag. Shyam had told himto carry a cloth bag with him and hewas sorry he did not listen to him.Somehow, he managed to reachhome with all his purchases (Fig.16.8).

Nanu’s friends enjoyed the feaston his birthday and played many

Fig. 16.8 Nanu with bags full of purchases

he saw the rag picking children nearhis house.

You might have seen somechildren, sorting the garbage nearyour house or at other places.Observe the children at work andfind out how they separate usefullmaterial from the garbage. They areactually helping us.

Talk to one such child and findout:

What do they do with the rubbishthey collect? Where do they take it?

Does he/she go to school? Whatabout his/her friends?

If they do not go to school, findout the possible reasons.

Can you help this child to readand write?

Have you ever helped at home tosell old newspapers, glass and metalthings, plastic bags and your oldnotebooks to a garbage dealer? Talkto him and find out what he doeswith all the garbage.

Would you like to make paperfrom old and discarded paper likeShyam? Let us learn to do this.

16.4 RECYCLING OF PAPER

You will require pieces of oldnewspapers, magazines, usedenvelopes, notebooks, or any otherpaper. Do not use shiny, plasticcoated paper. You will also need aframe fitted with a wire mesh or anet. You can also use a large sizedsieve in place of a frame.

Tear the paper into small pieces.Put them in a tub or a bucket andpour water in it. Let the pieces ofpaper remain submerged in water fora day. Make a thick paste of paperby pounding it.

games. All his friends wore the shinypaper hats Nanu had bought!

Shyam had made beautifulpapier- mâchè masks for Nanu’sfriends. He had a special gift for Nanuas well. A photoframe and a greetingcard made from the paste of all thepieces of paper Nanu had thrownaway! It was a new experience forNanu. All his friends went home withtheir masks. Nanu was too excitedto finish his meal and look athis gifts.

Nanu returned home, after hisholidays were over. How different histown was from Shyam’s village!There were no rag pickers in thevillage as it was neat and clean. Butnow he stopped making faces when

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Now, spread the wet paste on thewire mesh fixed to the frame. Pat itgently to make the thickness of layerof the paste as uniform as possible.Wait till water drains off. If requiredspread an old cloth or a sheet ofnewspaper on the paste to let it soakup the extra water.

Now, carefully remove the layer ofpaste from the frame, spread it on asheet of newspaper in the sun. Keepthe corners of the newspaper sheetpressed by putting some weights sothat these do not curl up.

You can add food colour, piecesof dry leaves or flower petals or piecesof coloured paper in the paste beforespreading it. It would help you to geta recycled paper with beautifulpatterns on it.

Can we recycle everything, just aswe recycle paper?

16.5 PLASTICS – BOON OR A CURSE?Some kind of plastics can berecycled, but, not all of them. Didyou notice that polythene bags andsome plastics did not rot in Activity1? You might now easily understandwhy polythene bags create a bigproblem in garbage disposal.

It may be a little difficult toimagine our life without plastics.Shall we list a few things we use thatare made of plastics? Toys, shoes,bags, pens, combs, tooth brushes,buckets, bottles, and water pipes —the list is very long. Can you name afew parts of a bus, car, radio,television, refrigerator and a scooterthat are made of plastics?

The use of plastics in itself mightnot create so much of a problem.Problems arise when we use plastics

excessively and are ignorant aboutways of disposing their waste. Thisis what is happening all aroundus! We might even be actingirresponsibly, knowing well about itsharmful effects.

We often use plactic bags to storecooked food items. Sometimes thesebags may not be suitable for keepingeatables. Consuming food packedin such plastic bags could be harmfulto our health. Many a timeshopkeepers use plastic bags thathave been used earlier for some otherpurpose. Sometimes bags collectedby rag pickers are also used afterwashing them. Use of such recycledplastic bags to keep food items couldbe harmfull for our health. Forstoring eatables we must insist onuse of plastic bags that are approvedfor such a use.

All kind of plastics give outharmful gases, upon heating orburning. These gases may causemany health problems, includingcancer, in humans. The governmenthas also laid down guidelines forrecycling of plastics.

Paheli would like to suggestthat containers used forstoring poisonous sub-stances should be recycledseparately and that suchrecycled plastics are notused to make plasticbags.


You must have noticed thatpeople often fill garbage in plasticbags and then throw it away. Whenstray animals look for food in thesebags, they end up swallowing these.Sometimes, they die due to this.

The plastic bags thrown awaycarelessly on roads and other placesget into drains and the sewer system.As a result, drains get choked and thewater spills on the roads. Duringheavy rains, it might even create aflood like situation. There is a lot ofharm that too much use of plasticscan do!

What can we do to minimise overuse of plastics and deal withgarbage?1. We make a minimum use of

plastic bags. We re-use the bagswhenever it is possible to do sowithout any adverse affects.

2. We insist shopkeepers use paperbags. We carry a cloth or a jutebag when we go out for shopping.

3. We do not use plastic bags tostore eatables.

4. We do not throw plastic bags hereand there, after use.

5. We never burn plastic bags andother plastic items.

6. We do not put garbage in plasticbags and throw it away.

7. We use vermicomposting at homeand deal with our kitchen wasteusefully.

8. We recycle paper.9. We use both sides of the paper to

write. We use a slate for roughwork. We use blank sheets ofpaper left in our notebooks forrough work.

10.We make our family, friends andothers to follow proper practicesfor disposing different kinds ofwastes.The most important point to know

and think about is that — moregarbage we generate, more difficultit will be to get rid of it.

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Key Words

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Landfill is an area where the garbage collected from a city or town is dumped.The area is later converted into a park.

Converting plant and animal waste including that from kitchen, into manure,is called composting.

The method of making compost from kitchen garbage using redworms iscalled vermicomposting.

Paper can be recycled to get useful products.

Plastics cannot be converted into less harmful substances by the process ofcomposting.

We need to generate less waste and find ways of dealing with the increasingamount of garbage in our surroundings.

1. (a) Which kind of garbage is not converted into compost by the redworms?

(b) Have you seen any other organism besides redworms, in your pit? If yes, try tofind out their names. Draw pictures of these.

2. Discuss :

(a) Is garbage disposal the responsibility only of the government?

(b) Is it possible to reduce the problems relating to disposal of garbage?

3. (a) What do you do with the left over food at home?

(b) If you and your friends are given the choice of eating in a plastic plate or abanana leaf platter at a party, which one would you prefer and why?

4. (a) Collect pieces of different kinds of paper. Find out which of these can berecycled.

(b) With the help of a lens look at the pieces of paper you collected for the abovequestion. Do you see any difference in the material of recycled paper and a newsheet of paper ?

5. (a) Collect different kinds of packaging material. What was the purpose for whicheach one was used? Discuss in groups.

(b) Give an example in which packaging could have been reduced.

(c) Write a story on how packaging increases the amount of garbage.

6. Do you think it is better to use compost instead of chemical fertilisers? Why?

Summary

Exercises


ACTIVITIES FOR DEALING WITH GARBAGE

1. Collect old and discarded objects and material like glass bottles, plastic bottles,coconut husk, wool, bed sheets, greeting cards and any other thing. Can youmake something useful out of these, instead of throwing them? Try.

2. Prepare a detailed project report on compost making activity you did in school.

A MATTER OF CONCERN!

In autumn lots of leaves are burnt in cities like Delhi. Some of the gasesproduced by burning leaves are similar to the gases released by the vehiclesmoving on the roads.

Instead of burning, if we make compost from these leaves, we can reduce theuse of chemical fertilizers.

The green areas which should have fresh air, actually become full of harmfulgases due to burning of leaves.

If you find any one is burning the leaves bring it to notice of municipal au-thorities or write to newspapers about it.

Generate social pressure against burning of leaves. Ensure that fallen leavesare not burnt but used for making compost.

Write to the ‘Tree Authority’ of your city or state to declare burning of leavesas an offence.

Documents

scert.goa.gov.in€¦ · Food : 1 Where Does It Come From? W hat did you eat at home today? Find out what your friend ate today. Did you eat the same kind of food yesterday and today?