1. Energy Transfer
Chapter 9

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

3. Three Methods of Energy Transfer
Conduction
Convection
Radiation

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

6. Convection
Convection current – flow of fluid due to heated expansion followed by cooling and contraction
Examples
Fire, candle
Warm air rises, cools, then flows downward
Wind current
Boil water in pot

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

8. Radiation Transfer of Energy 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

9. Energy Transfer from Sun
Electromagnetic energy is a type of energy that is radiated by the sun in the form of transverse waves vibrating at right angles to the direction of movement

10. Radiation occurs in different forms identified by their wavelength

12. Radiation is reflected – bounced back at the same angle they arrived
WHAT HAPPENS TO ELECTROMAGNETIC ENERGY (RADIATION) ONCE IT REACHES EARTH?
Radiation is reflected – bounced back at the same angle they arrived
Radiation is scattered – reflected in various directions
Radiation is refracted - bent
Radiation is transmitted – pass through the material
Radiation is absorbed (taken in as heat energy)
Radiation is reflected – bounced back at the same angle they arrived
Radiation is scattered – reflected in various directions
Radiation is refracted - bent
Radiation is transmitted – pass through the material
Radiation is absorbed (taken in as heat energy)

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