Lesson 4- Scientific Investigations.doc

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LESSON 4 - SCIENTIFICINVESTIGATIONS

When physicists observe a particular physicalphenomenon they will as questions as to how

or why it happens . A hypothesis will be putforth and experiments or scientificinvestigations will be carried out to prove ordisprove the hypothesis. If the experimentsbear out the hypothesis, the hypothesis maycome to regarded as theory or law of nature. Ifthe don’t the hypothesis will be rejected ormodified.In any experiment , the report on theexperiment will be based on these guidelinesand follows a sequence as shown in thefollowing flow chart

Inference

!arly assessment that is carried out to answerthe questions raised.

"he inference should be written as #######depend on########.$r"he #####..changes as the####...changes

Hypothesis

A general statement about the relationshipbetween a manipulated variable and aresponding variable.

"he hypothesis should be written as "he greater the###, the greater the##.$r"he bigger the####., the smaller the#..

Manipuate! "aria#e

"he quantity whose values we deliberately choose

to change or a primary variable which causes othersecondary variable to change.

$espon!in% "aria#e

"he quantity whose value depend on themanipulated variable or a secondary variable which changes in response to the change in themanipulated variable.

Fi&e! "aria#e

"he quantity whose value is %ept constantthroughout the experiment.

Ai'

A statement to show the investigation of thevariables involve.

"he aim of the experiment should be written as"o investigate the relationship between ###..and######

Apparatus

&ist the apparatus and materials used so that atleast a set of data for manipulated and respondingvariables can be determined.

'tate the arrangement of the apparatus that canfunction by drawing a labeling diagram .

(roce!ure

'tate the method of controlling the manipulatedvariables

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'tate the method of measuring the respondingvariables(epeat the experiments at least four times.

Ta#uatin% the !ata

(ecord the data in the following table

)anipulated variable (esponding variable

Anay)in% the !ata

*lot a graph of + (esponding variable against+)anipulated variable

Ho* to ta#uate the !ata +

"he table must be neatly drawn and the dataarranged in either and rows."he names and symbols of the manipulated andresponding variables must be written together withthe units.-or example,

elocity, v / s

"ime , t / s

olume , / m0 *ressure , * / *a

"he data shown in the table must be consistent inthe number of decimal places in accordance withthe respective measuring instruments.-or example,

&ength, l / cm "ime , t /s

1 23.4

3 35.6

7 08.7

6 53.3

4 95.1

If the data too small or too big use the standardform number.

-or example

"emperature θ /o: 21 31 01 71 51

;ensity, ρ / %g m


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All the points are mar%ed with a symbol such as across or circle and the centre of the cross mustaccurately positioned.

"he best straight line or the best curve graph mustbe drawn."he best straight line or the best curve graph is theline that passes through most of the points plottedsuch that it is balanced by the number of pointsabove and below the line. "he line also mustsmooth.

It is not advisable to plot graph by joining point topoint because the graph obtained is not smooth.

Ho* to anay)e the !ata +

+a ;etermine the relationship between twovariables.!xample

y is directly proportional to x.

or y α x

or y > %x % > constantor y > mx m > gradientor y2 > y3

x2 x3

y increases linearly with xor y > mx ? c

m > gradient c > intercept on axis gradient c > intercept on axis %

x % > constant

or y2 x2 > y3 x3

+b ;etermine the gradient of the graph

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!xample

;raw a sufficiently large triangle to calculatethe gradient of the graph.'tate value of the gradient with correct unit."he gradient of the graph is

m > y3 < y2

x3 < x2

> @( @(

+c ;etermine the certain values from the graph.

:ertain important values can be obtained fromthe graph plotted by drawing a horiontal lineor by extrapolating the graph.

+d 'tate the precautions should be ta%en-or example"he circuit connections must be ta%en$ff the switch when ta%ing the reading of themeters.)a%e sure the amplitude of oscillation is small.

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, Which of the following is the best way totabulate the data B

A oltage, 1 5 21 25 31

:urrent,I 1 2.9 3.5 0.7 7.3

"ime,t /s 3 7 6 4 21

;ensity,ρ /

%gm


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An experiment is carried out to find therelationship between mass and acceleration ofa trolley on a wooden runway."he experiment is repeated by adding thenumber of trolleys."he responding variable in this experiment is

A the length of the wooden runway. accelerationC mass

5 In a simple pendulum experiment, the lengthof the pendulum and time for 31 oscillationsare recorded."he length of the pendulum is a

A manipulated variable

responding variableC fixed variable

6 Dased on the graph above, what is the

gradient of the graphB

A < 2.5 < 1.9

C 1.9 . 2.1E 2.5

,7 What is the unit of the gradient of the graph

aboveB

A m m3

sC ms3 . ms< 3

,, A student plot a graph for a physical quantity ,@ on axis 21@ ? 5 * > 3@ ? 21C * > 5@ E 21

,4 "he following figure shows a graph F versus.

Which of the following shows the correctrelationship between F and B

A F > m ? m n

F > < m ? m nC F > m ? n n

. F > < n ? m m

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,1 "he pressure ,* of the gas is directlyproportional to the absolute temperature, " ofthe gas.When * > 211 ," > 51. What is the value of * when " > 711.

A 1.4A 235C 311 . 411E 3111

,2 Doyle’ s law state that the pressure of the gasis inversely proportional to the volume of thegas."he pressure of a bubble under sea surface is231 cm Cg *a and its volume is 25.4 cm0.When the bubble rises to the surface of thesea the pressure of the bubble is 96 cm Cg.

What is the volume of the bubble at thesurface of the seaB

A 21.1 cm0 35.1 cm0

C 237.4 cm0 . 018.2 cm0

E 599.3 cm0

, An object is released froma height , h and

the time ta%en to reach the ground is t.3

h/m 31 x

t/s 3 7

If h is directly proportional to t 3 , what is thevalue of x in the table above.

A 21 m 71 mC 41 m . 261 mE 371 m

,5 Gewton’s universal law of gravitation statesthat the gravitational force of attraction, -between two point masses is inverselyproportional to the square of the distance ,(between them.If the distance between them is 0(, what isthe gravitational force of attraction BA 8- 0-C - . -

0E -

8

,6 A student carries out an experiment to findout the relationship between the change inlength , y , of a spring and mass, m , of theload on the spring. "he arrangement of theapparatus for the experiment is shown in-igure 2 . "he length of the spring when aload is placed on the piston is l .

At the beginning of the experiment there is noload. "he length of the spring is l o . "he actuallength of l o is shown in -igure 3."he experiment is repeated by using load withmass , m , equal to 1.5 %g , 2.1 %g , 2.5 %g ,3.1 %g and 3.5 %g. "he actual lengths of thespring when the different masses are used areshown in -igure 0, -igure 7 , -igure 5 ,-igure 6 and -igure 9.

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+a Dased on the aim and the procedure ofthe experiment state the+i manipulated variable

HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

+ii responding variable

HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

+iii constant variable


+b )easure the length of the spring in

-igure 3.l o > HHHHHHHHHHHHHHHHHHH

)easure the lengths l of the spring in-igure 0 , -igure 7 , -igure 5 , -igure 6and -igure 9 when different load areused.

In each case, calculate the change inlength, y , of the spring where

y > + l o E l

"abulate your results for m ,l and y in thespace below.

+c $n the graph paper , plot a graph of yagainst m.

+d Dased on your graph, state therelationship between y and m .



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20 40 60 800

l /cm

1

2

3

4

5

T 2 / s

2Graph T 2 against l

100

l / cm


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/7 A student carries out an experiment toinvestigate the relationship between thelength of a simple oscillating pendulum ,l , with its period, T ."he experiment is repeated using differentlengths, l , and their corresponding periods,T , are recorded. A graph of T 2 against l , isthen plotted as shown above.+a Dased on the graph,

+i 'tate the relationship between T 2 with l .

################..

################..+ii :alculate period, T , when thelength

l > 75 cm.+'how your wor%ing

+iii :alculate the gradient of the graph.

+b Fsing the value of the gradient obtainedfrom +a+iii and the equation,

calculate the acceleration due togravity , g.

+c 'tate one precaution for this experiment.

##################

##################

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/, "he graph above represents graph Wagainst , where W and are the distanceson a wooden rod.

+a Dased on the graph state the

+i manipulated variable


+ii responding variable


+b :alculate the gradient of the graph.

+c ;etermine the intercept on

+i axis< W

....................................................

(ii) axis

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Lesson 4- Scientific Investigations.doc