8I Heating and cooling

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8I Heating and cooling

What is temperature?

Heat on the move

Energy waste


What a state!


What is temperature?



8I Temperature quiz


8I But what is temperature?

Temperature is a measure of ‘hotness’ or ‘coolness’. But what do we mean by ‘hotness’?

Well, we know if something is hotter than something else.

We can measure temperature (or ‘hotness’) using a thermometer.

The most common unit for temperature is degrees Celsius.

What is the temperature of boiling water in degrees Celsius?

And melting ice?


8I Heat and energy

Think of something that is used to remove heat from things.

To make something hotter you have to give it some energy.

This energy is called ‘thermal energy’ or ‘heat energy’.

So, a metal pan contains more heat energy when it is hot than when it is cold.

Cookers and fires are used to add energy to things – to heat things.


Heat on the move



8I Now we’re cooking!


8I But what is heat?

We know heat energy makes something hot. How does it do it?

Everything is made of small particles. In a solid these particles are held together quite tightly.

The particles can move by wobbling or vibrating in their fixed positions like bottles in a crate.

Heat energy makes the particles wobble more. We feel this increase in vibration as the object getting hotter.


8I Explaining conduction

What happens if we heat part of a metal rod?

The particles in that part of the rod vibrate more.

The particles pass on the vibration to other particles along the rod.The colder area warms up. We call this transfer of energy conduction.


1. Conduction happens when the vibrations of the particles in an object move from one particle to the next.

2. Conduction cannot happen in space because there are no particles to vibrate.

3. Particles that are closer together pass on vibrations less easily than particles that are far apart.

4. The difference in temperature between one area and another has no effect on the rate of conduction.

8I True conduction

Decide if these statements are true or false.

TRUE

TRUE

FALSE

TRUE


1. Most liquids cannot conduct heat well.

2. Gases conduct heat very well.

3. Metals tend to be better conductors of heat than plastics.

4. Heat is conducted along a metal bar as the metal particles move from the hot end to the cold end.

8I True conduction

Decide if these statements are true or false.

TRUE

FALSE

TRUE

FALSE


8I Convection

Think about the vibrating particles again… when they vibrate they take up more space. The object they are part of expands.

This happens in solids, liquids, and gases.

In liquids and gases the heated part is less dense.

So it floats up through the cooler liquid or gas above it.This is called convection.

How does this hot air balloon rise?

Can you think of another example of convection?


8I Watching convection

When you switch on a lava lamp it takes a while for the lava to start moving. Why?

Why does the lava start to fall here?

Why does the lava start to rise here?

Think about how a lava lamp works.


8I Radiation

Can you think of an example of heat transfer through empty space?

(Clue: think big!)

Radiation does not depend on particles to transmit the heat.

Heat energy is transferred as radiation even when no particles are present.


8I Radiation


8I Good radiators

Which ceramic mug of tea cools down fastest?

Can you think of another example of radiation?

These mugs of tea cool at different rates. Why?


Energy waste



8I Heat loss from a house

Losing energy costs money!

Study this table and then try our energy quiz.

Insulation method Money saved per year (£)

loft insulation (installing from scratch)

157

loft insulation (making it thicker) 40

double glazing 34cavity wall insulation 70draught excluders 8lagging hot water tank 11


1. Double glazing cuts down heat loss from a house because…

a) heat cannot pass through glass

b) the layer of air in the middle is a very good insulator

c) people can’t afford to turn the heating up after they’ve bought double glazing.

2. A well insulated loft cuts down heat loss because...

a) loft insulation does not let heat pass through easily

b) loft insulation is waterproof

c) loft insulation stops cold air leaking into the house.

8I Saving energy quiz


3. Which of the following should you do first to cut your heating bill?

a) fit loft insulation

b) fit double glazing

c) fit draught excluders. 4. Birds often sit on roofs of houses that do not have loft

insulation in winter. This is because…

a) the roofs feel warmer as heat rises from the house

b) the roofs tend to be flatter so the birds do not fall off

c) birds are allergic to the material used for loft insulation.

8I Saving energy quiz


What a state!



We can use the idea of particles to explain:

8I What a state!

how heat moves.

what happens to substances when they are heated.

Study these diagrams and then try our true-false quiz.

solid liquid gas


1. Particles in solids are much closer together than the particles in gases.

2. Particles in liquids cannot move around at all.

3. Solids hold their particles very tightly.

4. When a solid melts it is because the forces between the particles get weaker.

8I The truth about particles

True or false?

TRUE

FALSE

TRUE

TRUE


1. Gases conduct heat well because the particles are far apart.

2. When a solid melts the distance between the particles increases.

3. Liquids are difficult to compress because the particles are close together.

4. Gases can be compressed because there is so much empty space between the particles.

8I The truth about particles

True or false?

FALSE

TRUE

TRUE

TRUE

Date post:	20-Mar-2016
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8I Heating and cooling

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