0. Heat Transfer(write green)
How does the energy move from a hotter to a colder object?
Three mechanisms
Conduction
Convection
Radiation

1. Conduction Heat transfer in solids (contact heating)
Stir your hot soup with a metal spoon
Pretty soon you need a pot holder because the end of the spoon you are holding gets hot (Energy travels up the spoon from the end in the hot soup to the end in your hand)
This is heat(energy) transfer by conduction
Energy travels up the spoon from the end in the hot soup to the end in your hand
Conduction

2. Conduction
We sense the movement of energy by the increasing temperature
This means the atoms and molecules have higher average kinetic energy(movement)
This movement is due to electrons moving easily
The more easily the electrons can move, the better the conduction

3. Conduction
Metals have some electrons that are very loosely bound to the atoms in the material
Wood and plastic don’t have loosely bound electrons, so they are poor conductors

4. Good conductors
List some

5. Poor conductors
List some

6. Conduction

7. Conduction Air is a poor thermal conductor
If you stand in the sun on a cold winter day and are shielded from the wind, you stay pretty warm
Snow is a poor conductor, while water is better
Makes igloos a useful as a house

8. Will do this next

9. Convection Heat transfer in fluids (air is a fluid)
Instead of having energy moved by successive collisions of electrons, atoms and molecules, the fluid itself is set into motion called a current
These moving fluid currents are convectional currents

10. Convection

12. Convection
When the radiator heats the air, it becomes less dense and rises
Cool air moves in to replace the air that rose
This generates the air flow
So radiators don’t need a fan to stir the air and to distribute heat throughout a room
The rising air cools until its density matches that of the surrounding air

13. Convection
We take advantage of the cooling that occurs during an expansion
We make refrigerators and air conditioners operate by forcing gas under pressure through a small hole and expanding it into an empty space

14. Convection
Explains why breezes come from the ocean in the day and from the land at night

15. Radiation Energy carried by electromagnetic waves
Light, microwaves, radio waves, x-rays
Travels through space and energy is absorbed by objects atoms

16. Radiation
Every object is emitting electromagnetic waves regardless of temperature
Things we can see from their own radiation are very hot to have energy emitted in the visible region of the spectrum
Most things emit primarily in the infrared
Night vision goggles, etc.

17. Radiation Interior of a car on a sunny day
Sunlight comes in as visible light
Seats and interior are much cooler so they radiate in the infrared instead of visible
Glass in the windows blocks infrared so energy can’t get out
Car interior heats up!

18. Radiation A good absorber reflects very little energy, HEATS quickly
Think about dark pavement
A poor absorber reflects a lot of energy, stays cooler
Think about snow that doesn’t melt in sunshine even though 1400 watts/meter2 are hitting it,,

19. Radiation At night, objects receive no input energy from the sun
But, they are warmer than outer space, so they continue to radiate energy
Thus, they cool off
Can we make ice in the desert without a refrigerator?

22. Newton’s Law of Cooling
Rate of cooling(heating) of an object is proportional to the temperature difference between an object and its surroundings
The greater the difference in temperature of two objects, the faster the heating/cooling