1. Transfer of Energy

2. Heat Transfer
Heat Energy is transferred from hotter object to colder object
Examples?
Cooking pasta
Making ice
Making popcorn
Roasting marshmallows

3. Conduction 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
This is heat transfer by conduction
Energy travels up the spoon from the end in the hot soup to the end in your hand by direct contact!

4. Conduction Transfer E as heat between particles in direct contact
Example
Roasting marshmallow with wire
Air molecules collide with wire
Transfer energy to wire
Particles in wire move faster, have more E
E then transfer to hand, detect warmth

5. Conduction
For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon.
Fun fact: Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. You perceive the heat that is leaving your hand as cold.

6. Conduction

7. Conduction Example Put your hand on the desk. Popcorn in a pot
How does it feel?
Is it colder or is the heat transferring by CONDUCTION?
Popcorn in a pot
The heat is transferred by direct contact from the pan, to the oil, to the kernels of popcorn.

8. Convection
Energy transfer through movement of fluids at different temperatures due to density
(fluids - liquids and gases)
Examples
Camp fire
See soot, embers rise & swirl
Rise upwards – warm air expands
Why?

9. Convection
Convection current – flow of fluid due to expansion caused by heat followed by cooling and contraction
Examples
Wind current
Boil water in pot

10. Convection
You can hold your fingers beside the candle flame without harm, but not above the flame. Why?

11. Convection Examples Water…boiling Hot air popcorn What is happening?
The hot air transfers the heat to the cooler kernels, and when enough hot air heats the kernels they pop.

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

13. Radiation Transfer of E by electromagnetic waves
No movement of matter – will work in vacuum or outer space
No contact or movement of fluid
Infrared, visible light, UV rays
Example
Fire emits radiation (infrared), skin absorbs E, increase in temperature

14. Radiation Radiation can be absorbed and emitted Color
Summer day: wear light or dark clothes?
Winter day: wear light or dark clothes?
Why?

15. 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!

16. Radiation
Radiation: Electromagnetic waves that directly transport ENERGY through space
Sunlight is a form of radiation that travels through space to our planet without the aid of fluids or solids. The energy travels through nothingness! Just think of it! The sun transfers heat through km of space.
Because there are no solids (like a huge spoon) touching the sun and our planet, conduction is not responsible for bringing heat to Earth.
Since there are no fluids (like air and water) in space, convection is not responsible for transferring the heat.
Radiation brings heat to our planet.

17. What type of heat transfer is involved?
Heating a room with a fireplace
Egg cooking in a frying pan
Roof of a house becoming hot

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