Energy Is Never Used Up

0:00When a device uses energy, is that energy used up?

0:05Say 100 joules of electrical energy flows into an old-style filament bulb.

0:11About 10 joules comes out as light.

0:15About 90 joules comes out as heat.

0:18Add them up: 10 joules plus 90 joules makes 100 joules.

0:24So the energy that comes out equals the energy that went in.

0:29Energy is never created or destroyed, so we say energy is conserved.

0:36The wasted heat is not gone; it spreads out into the room.

0:41Other everyday devices change energy from one form to another too.

0:46A fan changes electrical energy into kinetic energy, plus some sound and heat.

0:52A solar panel changes light into electrical energy and heat.

0:57A flashlight changes the chemical energy in its battery into light and heat.

1:02Energy is never used up; it only changes from one form to another.