1. Transmission of Heat

2. Conduction n Heat transfer due to direct contact n Either between different materials in thermal contact or different parts of the same material n Materials that conduct heat well are good conductors, usually metals n Collisions between atoms, molecules, and electrons transfer energy

3. Conduction n Metals make good conductors because of many “loose” outer electrons n Materials that don’t conduct well are insulators n Liquids & gases usually good insulators n Insulating materials often have enclosed air spaces to delay heat transfer

4. Convection n Heat transfer due to current in a fluid n Warm fluid actually moves, changes position n Warmer areas expand, are less dense and rise n Convection currents create wind, weather patterns, sea breezes

5. Radiation n Transfer of energy by electromagnetic waves n Can transfer heat through vacuum of space n Objects emit energy depending on temp -- low temp means long waves, low energy n High temp objects emit high energy short waves

6. Radiation n Infrared waves are absorbed by our skin and produce sensation of heat n Heat lamps emit infrared radiation Hotter objects emit visible light as well, starting at red (500 o C) moving to white hot (1200 o C) as more colors are added to radiation Hotter objects emit visible light as well, starting at red (500 o C) moving to white hot (1200 o C) as more colors are added to radiation

7. Absorption of Radiant Energy n Radiation either absorbed or reflected n Good absorbers are poor reflectors and appear dark n Good reflectors appear light, absorb little energy and remain cool

8. Emission of Radiant Energy n Good absorbers are good emitters of energy and vice versa n Dark objects absorb and emit energy well n Rate of cooling is proportional to temp difference with surroundings: Newton’s Law of Cooling n Same law applies to heating

9. Greenhouse Effect n Earth absorbs radiant energy from sun n Earth emits terrestrial radiation into space n If rates of absorption and radiation are equal, temp remains constant n Greenhouse effect is effect of atmospheric gases on balance of absorption-emission

10. Greenhouse Effect n High energy short waves from sun reach earth and are absorbed n Earth emits longer waves (because it’s cooler) n Longer waves are absorbed by carbon dioxide and water vapor in atmosphere n Energy is trapped by atmosphere and earth warms

11. Greenhouse Effect n If carbon dioxide levels increase, global warming can occur n Effect is similar in greenhouse -- glass is transparent to short waves from sun but reflect long waves back into greenhouse