It never goes anywhere
Where Does Energy Go When Things Stop?
Energy is never used up or destroyed; it only ever changes into a different form.
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Step 1 of 5
Stopping looks like energy disappearing.
A rolling ball slows and halts, a bouncing ball settles, a spinning wheel stops. In each case the movement seems simply to vanish.
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Step 2 of 5
It always turns into something else.
Rubbing against the ground makes heat, air makes sound, and the ball itself flexes. Add those up and the movement is fully accounted for.
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Step 3 of 5
Energy has many forms and swaps between them.
Height, movement, heat, sound, light, chemical energy in food and fuel — all the same currency in different shapes.
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Step 4 of 5
The total never changes.
Careful measurement always finds exactly as much energy afterwards as before. Nothing is created and nothing is destroyed anywhere.
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Step 5 of 5
Everything drifts towards heat.
Every transfer spills a little as heat, and heat is the hardest form to use again. That is why nothing keeps moving forever.
Every joule ever released still exists, mostly as very slightly warmer surroundings, spread too thinly to be useful.
The short version
Energy is never used up or lost; every transfer changes its form, and each change spills some as heat that is hard to use again.
Try it yourself
Bend a paperclip back and forth twenty times, then touch the bend. The effort you put in is sitting there as warmth.
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