Where the Energy Goes
- Physics
- Ages 11–14 · Grades 6–8
- Hands-on experiment
What you’ll find out
- Energy changes form rather than being created or destroyed.
- Energy that appears to be "lost" has usually been spread out as heat.
- Tracking energy through a system explains why no machine is perfectly efficient.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Energy changes its form
A battery stores chemical energy. Put it in a torch and you get light out. That light did not come from nowhere — the energy changed form, from chemical to electrical to light and heat. Energy does this constantly. It moves between objects and changes between forms, but it does not appear from nothing or disappear into nothing.
The energy you think you lost
Rub your hands together and they get warm. That warmth came from the movement of your hands. When you brake on a bicycle, it slows down — and the energy of that movement did not disappear, it became heat in the brake pads. Whenever energy seems to have been lost, look for heat. It is nearly always where it went.
Why nothing is perfectly efficient
Every machine wastes some energy. Motors get warm; phones get warm while charging. That heat is energy that did not do the job you wanted it to do. No machine converts all its input into useful work — some always escapes as heat. That is exactly what it means to say nothing is 100% efficient.
Curriculum links: NGSS MS-PS3-5 · NGSS MS-PS3-3