1. 21.2 Heat

2. Heat is thermal energy that is transferred from one object to another, when the objects are at different temperatures Heat is thermal energy that is transferred from one object to another, when the objects are at different temperatures Amount of energy transferred depends on the temperature difference Amount of energy transferred depends on the temperature difference

3. Transfer of heat When heat is transferred thermal energy ALWAYS moves from warmer to cooler When heat is transferred thermal energy ALWAYS moves from warmer to cooler Warmer loses thermal energy Warmer loses thermal energy Cooler gains thermal energy Cooler gains thermal energy Process stops when the two temps are the same Process stops when the two temps are the same

6. Conduction Conduction occurs when the materials of two materials are in direct contact Conduction occurs when the materials of two materials are in direct contact The particles of one material collide with the particles of another material and energy is transferred The particles of one material collide with the particles of another material and energy is transferred Results in the molecules of the cooler material gaining energy and therefore temperature. Results in the molecules of the cooler material gaining energy and therefore temperature. Occurs most easily between solids and liquids, where atoms are closer Occurs most easily between solids and liquids, where atoms are closer

9. Convection Convection requires the molecules to move to transfer energy. So can only take place in liquids or gases Convection requires the molecules to move to transfer energy. So can only take place in liquids or gases Molecules gain energy, expand, become less dense, rise, cool, increase in density, fall, reheated …. Repeat process Molecules gain energy, expand, become less dense, rise, cool, increase in density, fall, reheated …. Repeat process

10. Natural Convection Convection occurs in nature when warmer lass dense fluids are replaced by cooler more dense fluids Convection occurs in nature when warmer lass dense fluids are replaced by cooler more dense fluids –Happens to the air on a warm day –Sea breeze to land

12. Forced Convection Here outside forces push a fluid, to make it move and transfer heat Here outside forces push a fluid, to make it move and transfer heat –Fan in an engine is an example

13. Radiation Radiation occurs energy is transferred by electromagnetic waves Radiation occurs energy is transferred by electromagnetic waves Waves can carry energy through the vacuum of empty space as well as though matter Waves can carry energy through the vacuum of empty space as well as though matter Sources of radiation – warm objects emit more then cooler objects Sources of radiation – warm objects emit more then cooler objects

16. Thermal Conductors Conductor is any material that easily transfers heat. Conductor is any material that easily transfers heat. –Types of atoms or chemical bonds –Metals have loose electrons that allow transfer of heat

17. Thermal Insulators Insulator is a material which does not allow heat to pass through it easily Insulator is a material which does not allow heat to pass through it easily –Liquids and gases are usually good insulators because of the space between molecules, makes heat transfer harder

18. Heat Absorption Heat absorption is different for different material, this effects the change in temperature for that material in a particular situation Heat absorption is different for different material, this effects the change in temperature for that material in a particular situation Specific Heat Capacity– the amount of heat needed to raise the temperature of 1Kg substance by 1C Specific Heat Capacity– the amount of heat needed to raise the temperature of 1Kg substance by 1C

19. The more heat needed the higher the specific heat The more heat needed the higher the specific heat Objects with a higher specific heat are slower to warm up but also slower to cool down Objects with a higher specific heat are slower to warm up but also slower to cool down

20. Thermal Pollution Increase in temperature of a body of water caused by adding warmer water to that body Increase in temperature of a body of water caused by adding warmer water to that body Effects – causes increase use of oxygen Effects – causes increase use of oxygen -Organisms become more sensitive to pollutants - Reducing thermal pollution could b achieved by cooling the water from factories in cooling towers

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