7.1 Heat is a form of energy

7.2 Heat flow and its effect

7.3 The effect of heat on matter

7.4 Applying the principles of expansion and

contraction of matter

7.5 Dark, dull objects absorbs and gives out heat

better

7.6 Appreciating the benefits of heat flow

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CHAPTER 7

Heat

State that the sun gives out heat

State other sources of heat

State that heat is a form of energy

Give examples of the uses of heat

State the meaning of temperature

State the differences between heat an temperature

7.1 Heat as a Form of Energy

The Sun

Primary source of heat

We feel cold

during the night

We feel hot

during the day

time

Most of the heat around the

earth comes from the sun

Burning objects Electricity that runs

through a coiled wire

Heat can also be

produced by rubbing

two objects together

•Keep us warm

•Dry clothes

•Causes water to evaporate to form clouds

•Causes breeze

•Produces solar energy

Examples

of the uses

of heat in

our daily lfe

Incubating eggs

Boiling Water

Drying Clothes

Distillating petroleum

Cooking

Drying hair

Temperature

Temperature is a measure of the degree of hotness of an object or

substance

The unit for temperature is degree Celcius (oC)

The temperature of a substance will increase if heat is supplied to it

The temperature of a substance will drop if heat is removed

Heat TemperatureA form of energy A degree or measurement of hotness

or coldness of a substance

The unit of measurement is Joule (J) Measured by using a thermometer.The unit of measurement is degree

Celcius (oC) or Kelvins (K)

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CHAPTER 7

Heat

State that heat causes solids, liquids and gases to

expand

State that heat flows in Three different ways

(Conduction, Convection, and radiation)

State that heat flows from hot to cold

Give examples of heat flow in natural phenomena

List uses of heat conductors and heat insulators

in daily life and carry out an experiment to

investigate different materials as heat insulators

7.2 Heat Flow and its Effect

Heat causes solid, liquids and gases to expand

Heat causes the particles of a substance to move faster. As the

particles move faster, they take up more space.

Movement of particle at

lower temperature

Movement of particle at

higher temperature

This causes the solid to expand (Gets bigger)

Heat flows in 3 different ways

• Conduction

• Convection

• Radiation

Conduction

When one end of a metal bar is

heated by a candle flame,

the particles of the metal bar

near the flame receive extra

heat energy from the flame

The particles vibrate more

vigorously and transfer energy

to the particles next to them

Heat flows in 3 different ways

ConvectionWhen gas, such as air, is

heated, the air expands.

The hot air becomes less dense

and rises.

As the warm air rises, cooler air

rush in to take its place.

In the same way, heat is carried

by convection in liquids

Cool Air Hot Air

Heat flows in 3 different ways

Radiation

Heat travels through empty

space ( vacuum) as radiation, or

heat rays. They travel very fast

through space.

Radiation is the transfer of heat

energy in the form

electromagnetic waves without

medium.

Heat flows in natural phenomena

Land Breeze (At night)

Sea Breeze (During the day)

At night the sea is warmer than the land

The less dense hot air from the sea rises

Cool air from the land flows to the sea as

land breeze

During the day, the land is warmer than

the sea

The less dense hot air on land rises.

Cool air from the sea flows towards the

land as sea breeze

Heat conductors & Insulators

Solids that allow heat pass through easily are called heat conductors

Good heat conductors are usually METALS

Solids that does not allow heat pass them easily are called heat insulators

Good heat insulators are usually Wood, plastics and glass

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CHAPTER 7

Heat

State the change in state of matter in physical processes

Explain that the change in state of matter involves

absorption and release of heat

Give examples of daily observations which show a

change in state of matter

7.3 The Effect of heat on matter

Melting & Freezing

Matter can change from one state to another by heating or cooling it

A change in the state of matter involves the absorption or loss of heat

(heat absorbed)

melting

freezing

(heat released)

When heat is absorbed particles

gain energy

When heat is released

particles loses energy

SOLID

GASLIQUID

Evaporation / Boiling

Condensation

SOLID

GAS

LIQUID

Heat is released

Particles of matter

losses energy

Particles move slower

and slower

Particles are getting

so close together

Heat is absorbed

Particles of matter

gains energy

Particles

vibrates/move faster

If heat is provided

continuously, particles

move further and

further apart

Explain with examples the use of expansion and contraction of

matter in daily life

Apply the principles of expansion and contrtaction of matter in

solving simple problems

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CHAPTER 7

Heat7.4 Applying the principles of expansions and

contraction of matter

MatterMatter EXPANDS when heated and CONTRACTS when cooled

Gap

Mercury Thermometer

Mercury expands and rises in response to changes in temperature

Rollers are used in bridges to allow expansion during hot days

State that dark, dull objects absorb heat better than white, shiny

objects

State that dark, dull objects give out heat better than white , shiny

objects

Carry out experiments to investigate heat absorption and heat

release

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CHAPTER 7

Heat7.5 Dark, dull objects absorb and give out heat

better

The ability of an object to absorb or give out

heat rays depends on the

surface condition of the object

Dark, dull objects absorb heat

better then white, shiny

objects.

Dark, dull objects give out heat

better then white, shiny

objects.

Applications of the Principle of Radiation and

Absorption of Heat

White – Coloured and bright clothes are suitable to wear during

hot days because the white or bright surface reflects heat well.

Therefore, the wearer does not feel too hot.

Buildings – in tropical countries are normally painted white to

reflect heat and for the interior to remain cool

Petrol tanks – of oil tankers are usually painted with aluminium to

reflect heat from sunlight and as a result prevent the petrol from

becoming too hot.

Thermos flask – are equipped with special features to retain the

hotness or coldness of a liquid for a longer period of time

Car radiators – are painted dull black to enable hot water inside

to reflect heat more effectively

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