8I Heating and cooling

1. 8I Heating and cooling 8IHeating and cooling What is temperature? Heat on the move Energy waste What a state!

2. 8I Heating and cooling What is temperature?

3. 8I Temperature quiz

4. 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?

5. 8I Heat and energy 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. Think of something that is used to remove heat from things.

6. 8I Heating and cooling Heat on the move

7. 8I Now we’re cooking!

8. 8I But what is heat? 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. We know heat energy makes something hot. How does it do it?

9. 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.

10. 8I True conduction Decide if these statements are true or false. 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. TRUE TRUE FALSE TRUE

11. 8I True conduction Decide if these statements are true or false. 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. TRUE FALSE TRUE FALSE

12. 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?

13. 8I Watching convection Why does the lava start to fall here? Why does the lava start to rise here? Think about how a lava lamp works. When you switch on a lava lamp it takes a while for the lava to start moving. Why?

14. 8I Radiation Radiation does not depend on particles to transmit the heat. Heat energy is transferred as radiation even when no particles are present. Can you think of an example of heat transfer through empty space? (Clue: think big!)

15. 8I Radiation

16. 8I Good radiators These mugs of tea cool at different rates. Why? Which ceramic mug of tea cools down fastest? Can you think of another example of radiation?

17. 8I Heating and cooling Energy waste

18. 8I Heat loss from a house Losing energy costs money! Study this table and then try our energy quiz.

19. 8I Saving energy quiz 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.

20. 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.

21. 8I Heating and cooling What a state!

22. 8I What a state! how heat moves. what happens to substances when they are heated. We can use the idea of particles to explain: Study these diagrams and then try our true-false quiz. liquid gas solid

23. 8I The truth about particles True or false? 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. TRUE FALSE TRUE TRUE

24. 8I The truth about particles True or false? 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. FALSE TRUE TRUE TRUE