Lss module 1 chpt 3 investigating heat

MODULE 1:GADGETS WORK WONDERS (I)Chapter 3 Investigating Heat

© Copyright Star Publishing Pte Ltd

Chapter 3 Investigating Heat

3.1 What is temperature and how is it measured?

3.2 What is heat and why is it important?

3.3 Why can expansion and contraction be both useful and harmful?


ObjectivesUnderstand that temperature is a

measure of the degree of hotness and coldness of an object

Recognise that there are different types of thermometers (digital thermometer, laboratory thermometer and temperature sensors)

Measure temperature using a thermometer or a datalogger with temperature sensors


TemperatureTemperature is a

measure of the degree of hotness or coldness of an object.

In Singapore, temperature is usually measured in degree Celsius (°C).

We use a thermometer to measure temperature reliably and safely.


using our sense of touchto determine temperature

may not be accurate

Thermometers – Liquid-In-Glass Thermometers

The liquid-in-glass thermometer consists of a round glass bulb which contains liquid and a narrow glass tube.

The stem of the thermometer is marked with a scale.

Alcohol and mercury are used in this type of thermometer.

For daily uses, alcohol is preferred as it is safer than mercury which is poisonous.


a liquid-in-glass laboratory thermometer

How does a Liquid-In-Glass Thermometer work?

When the thermometer is placed in a hot place, the liquid in the bulb will expand and move up the narrow tube.

The opposite happens when the thermometer is placed in a cold place. The liquid will contract and move down the narrow tube.

The position where the liquid stops indicates the temperature which can be read from the scale.


Digital Thermometers

Digital thermometers do not use liquids to measure temperature. Instead of reading the temperature from a scale, the temperature is displayed directly.

Three common types of digital thermometers are:

(a) digital oral thermometer(b) infrared ear thermometer(c) infrared non-contact thermometer


a digital oral thermometer

Digital thermometers


Infrared earthermometer

Infrared non-contactthermometer

Dataloggers A datalogger with a

temperature sensor is used to keep track of temperature over a period of time.

The datalogger measures and records the temperature at preset intervals over a period of time.


datalogger withtemperature sensor

Activity Book LinkActivity 3.1How Hot is the Water?Activity 3.2Hot and Cold Log






ObjectivesExplain that heat is a form of energy

that flows from a hotter to a colder region

Recognise that when the temperature of a substance increases, the substance has absorbed heat; when the temperature of a substance decreases, the substance has lost heat

State the importance of heat energy in our life


What is Heat Energy?

Heat is a form of energy that flows from a hotter to a colder region.

In the diagram on the left, the hotter block will become cooler while the cooler block will become hotter until both blocks have the same temperature.


two iron blocks at different

temperatures

two iron blocks at different

temperatures

What is Temperature?

Temperature is the measure of the degree of hotness of an object.

Temperature tells us how hot or cold an object is.

The amount of heat energy an object has depends on both its mass and temperature.

The higher the temperature of an object, the more heat it has. © Copyright Star Publishing Pte Ltd

the water in Beaker B has more heat energy as its mass is greater

Temperature change

When an object gains heat, its temperature will increase. On the other hand, when the object loses heat, its temperature will decrease.

However, there will be no change in temperature when a substance is changing its state (e.g. Melting or boiling), even when heat is gained or lost.


when the water in the pot

gains heat, its temperature increases

when the cans of drink lose heat, their temperature

decreases

Importance of Heat EnergyHeat is important to

us.

(a) Heat is used to cook our food, making it safe to eat.

(b) In cold countries, heat is used to keep homes warm during winter.


a fireplace provides warmth from burning wood

Importance of Heat Energy

(c) Heat is used to dry things quickly.

(d) Heat is used to kill germs.


clothes dry quicklyunder the sun

sterilising baby milk bottles with steam

Importance of Heat Energy

(e) Heat is needed in industrial processes. During welding, heat is used to melt two pieces of metal. When they have cooled down, the two pieces of metal will be joined together strongly.

(f) Heat is used to refine metals.


welding of metal makes use of heat

metal rods being refined in a huge burner

Activity Book LinkActivity 3.3Usefulness andHarmfulness of Heat






ObjectivesInfer that generally solids, liquids and

gases expand when heated and contract when cooled

Describe some consequences and applications of expansion and contraction in everyday life

Appreciate science for its usefulness in improving quality of life—knowledge of heat allows us to tap on its usefulness and reduce its harmful effects


Expansion and Contraction

One way to open the tight metal cap of a bottle is to heat up the cap. The cap will expand and become loose.


using expansion to open a tight bottle cap

Expansion and Contraction of Solids


Activity Book LinkActivity 3.4Expansion and Contraction of Solids

Expansion and Contraction of Liquids

Liquids also expand when they are heated and contract when they are cooled.

Generally, liquids expand more than solids when heated and contract more when they are cooled


Activity Book LinkActivity 3.5Expansion and Contraction of Liquids

Expansion and Contraction of Gases

Gases expand when heated and contract when cooled.

Generally, gases expand more than solids and liquids when heated. Gases contract more than solids and liquids when cooled.


air expands when heated and contracts when cooled

Activity Book LinkActivity 3.6Expansion and Contraction of Gases

Effects of Expansion and ContractionExpansion and

contraction involve very large forces which can cause harm and damage to buildings and structures.

Railway tracks are often laid with gaps to allow spaces for expansion and to prevent buckling.


railway tracks that havebuckled under the hot sun

In HDB estate, there is a requirement for gaps between floor tiles to be between 2 mm and 4 mm* to allow for expansion in hot weather.

Otherwise, the tiles will crack and pop out when they expand.


expansion gaps between floor tiles in HDB estates

The force of contraction can also cause damage.

Overhead cables are installed with extra length so that they will not snap when they contract during cold weather.


overhead cables contract when they are cooled

Benefits of Expansion and Contraction

Expansion and contraction are used in riveting and bimetallic strips.


bimetallic strips are used in thermostats to control temperature such as in rice cookers, electric irons and electric ovens

Riveting


Riveting is a method used to hold two pieces of metal tightly together

What is a bimetallic strip?A bimetallic strip

consists of two strips of different metals joined together.

At room temperature, the strip is flat. When heated or cooled, the bimetallic strip will bend.


a thermostat which is used tocontrol the temperature of an oven

Bimetallic StripWhen heated, the

brass strip expands more than the iron strip, causing the bimetallic strip to bend.

When cooled, the brass strip contracts more than the iron strip, causing the bimetallic strip to bend in the opposite direction.


a bimetallic strip made of brass and iron


Education

Lss module 1 chpt 3 investigating heat