1. Conduction, Convection and Radiation

2. Radiation: heat transfer via radiant energy  Radiant energy is in the form of electromagnetic waves

3. All substances, at any temperature above absolute zero, emit radiant energy.  We don’t run out of energy because: ○ Energy can neither be created nor destroyed ○ All things also absorb energy  Dark objects absorb a lot of energy, but also radiate a lot.  If a surface is hotter than its surroundings it will be a net emitter and will cool.  If a surface is cooler than its surroundings it will be a net absorber and will warm.

4. The Sun’s Radiant Energy  The sun has a very high temperature and emits a high frequency of radiant energy.  Energy comes from nuclear reactions

5. Terrestrial Radiation: the earth’s radiation  The earth has a comparatively low temperature and emits a lower frequency.  Energy comes from radioactivity in the earth’s interior

6. Conduction: heat transfer via particle (e-) collision  Solids are good conductors because particles are closer together  Metals are the best conductors of thermal energy ○ Metal atoms have loosely held electrons  Poor conductors are called insulators ○ Insulators have tightly held electrons

7. Convection: heat transfer via movement of a fluid  As fluids near the bottom are heats they begin top move faster. This causes them to spread apart and become less dense.  Less dense water rises away from the heat source and cooler fluid moves down towards it.

8. Convection in Nature  During the day the land is warmer than the water  During the night the water is warmer than the air.

9. Evaporation, Condensation, Boiling, Melting and Freezing

10. Energy is Needed for a Phase Change  Whenever a substance changes phase, an energy transfer occurs. ○ Heat of Fusion: amount of energy needed to change a substance from a solid to a liquid (melt) ○ Heat of Vaporization: amount of energy required to change a substance from a liquid to a gas (boil) Solid Liquid Gas Energy is absorbed when change of phase is in this direction Energy is released when change of phase is in this direction

11. Practice Problems: The heat of fusion of water is 335 kj/kg.  How much energy must be absorbed to melt 1 kg of ice? 335 kj  How much energy must be released to freeze the water back into ice? 335 kj

12. There is no temperature change during a phase change! Energy is going into the change in phase not into eating up the substance!