Heat Transfer

1
Heat Transfer

• How does the energy move from a hotter to a
  colder object?
• Three ways/types/mechanisms
• Conduction
• Convection
• Radiation

2
Conduction

• This is heat transfer by touching!
• One molecule hits another and increases its
  motion. (atoms or molecules interact)
• The flow of thermal energy through a substance
  from a higher- to a lower-temperature

3
Conduction Example
Energy travels up the spoon from the end in the
hot soup to the end in your hand
Stir your hot soup with a metal spoon
hot!
Pretty soon you need a pot holder because the end
of the spoon you are holding gets hot
4
How does these show Conduction?
Pan touch burner (conduction)--Food touch pan
(conduction) food molecules cook
Oven mit protects hand from conduction
Heat from foot goes to warm cold floor
5
Convection

• Heat Transfer in FLUIDS (GAS OR LIQUID)
• the GAS OR LIQUID itself is set into motion
  called a current
• These moving fluid currents are convection

6
Convection
heat transferred by
circulation
the of a fluid
7
Convection at home

• 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
• The rising air cools until its density matches
  that of the surrounding air

8
Convection outside

• Explains why breezes come from the ocean in the
  day and from the land at night

9
Radiation

• Energy carried by electromagnetic waves that can
  TRAVEL Through EMPTY SPACE!
• radio waves, microwaves, infrared, VISIBLE LIGHT,
  ultraviolet, x-rays, gamma

10
Radiation

• Without the sun there would be no weather, food
  life!
• The suns radiates energy as ultraviolet,
  infrared, and visible
• If you were standing next to the camp stove, you
  would be warmed by the radiation given off by
  flame.

11
Radiation examples
Heat from stove radiates to warm Fido!
Heat radiates from camp fire to cook marshmallow
Light bulb radiates heat as it creates light!
12
Radiation

• A good absorber reflects very little energy
• Think about dark pavement and/or sand on beach
• A poor absorber reflects a lot of energy
• Think about snow that doesnt melt in sunshine