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 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

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)

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