2. 1 Y10 Science Heat and Energy

3. 2 Insulation Aims: Describe how insulation is used to reduce energy transfers from buildings and the human body. Understand that many insulating materials make use of the insulating properties of air that is not free to form convection currents.

4. 3 Different heat transfers Conduction - movement of heat due to a difference in temperature Convection - when heat is carried away by moving fluid Radiation - emission of energy by electromagnetic waves Convection Conduction Radiation

5. 4 Conduction Conduction is the method of heat transfer in solids. If you touch the handle of a metal saucepan that has been heated, the heat from the saucepan will conduct along the metal handle into your hand. The heat energy conducts along the handle to your hand

6. 5 Conduction Insulation works because of the air space… foam, fibre glass, double glazed windows. Poor conductors are called insulators. Wood, snow and gases are excellent insulators.

7. 6 Convection Convection is the method of heat transfer in liquids and gases. The warm air above the saucepan rises as it is less dense than the cooler air above it. Less dense warm air rises through more dense cooler air

8. 7 Convection currents The air reaching land is heated, the air becomes hotter, the air particles move faster, the air expands, becomes less dense and rises. The air then cools, its particles move slower, it contracts, becomes more dense and falls. fff

9. 8 Radiation Radiation is the only method of heat transfer that does not require particles as a medium. This means it is the only method of heat transfer that can travel through a vacuum. Heat radiation is emitted by all objects above absolute zero and travels in straight lines.

10. 9 Why is black cool? The black smock absorbs infra red radiation from the Sun and becomes hot. It heats the air inside and causes a convection current. Cool air is pushed in the bottom. Although the air and garment are hot the movement of air keeps the person cool.

11. 10 CONDUCTION Heat moves from the hotter object into a colder object that directly touch it.

12. 11 CONVECTION Heat is carried away by the air – heated air rises away, and lets cooler air fall.

13. 12 RADIATION Heat energy is radiated from a hot object. You can see it using an infra-red camera.

14. 13 CONDUCTION CONVECTION RADIATION

15. 14 Home insulation Heating and cooling our homes is our greatest energy expense

16. 15 Roof insulation Air is an excellent insulator. Fibreglass is an excellent material for trapping small amounts of air. A two or four inch layer of fibre glass insulation in you roof will pay for itself within a year.

17. 16 Cavity wall insulation Most walls have two layers of bricks with a gap or ‘cavity’ in between. This cavity lets air move around – energy is lost by convection and conduction. Filling the gap with an air bubble filled foam reduces the heat lost.

18. 17 Wall heat loss 100J 70J 55J 40J A B C Three identical houses, apart from their walls, were measured to see how much heat was lost in a certain time… Which house lost the most heat energy? Which house lost the least energy?

19. 18 Window insulation Double glazed windows trap a small amount of air between two panes of glass. The air cannot move very much so energy loss by conduction through the glass is reduced.

20. 19 Summary - Insulation We can insulate objects, including ourselves, to reduce energy transfers from hot objects to cooler objects. Air is often used as an insulating material. Air is a bad conductor. Air must be trapped in small bubbles to stop it moving around. If air can move around it will transfer energy by convection. Common ways of insulating our homes include: roof insulation, cavity wall insulation, carpets, curtains and double glazing.