Energy Transfer

Chapter 9

Energy Transfer

• Energy is transferred from hotter object to colder object

• Examples?– Cooking pasta– Making ice– Making popcorn– Roasting marshmallows

Three Methods of Energy Transfer

• Conduction

• Convection

• Radiation

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

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?

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

Convection

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

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

Energy Transfer from SunEnergy 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

Radiation occurs in different forms identified by their wavelength

• 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)

Radiation

• Radiation can be absorbed and emitted

• Color– Summer day: wear light or dark clothes?– Winter day: wear light or dark clothes?– Why?