Conservation of energy
Energy is never made or destroyed. It is only moved from one store to another or spread out.
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Analogy
Like water poured between jugs: some may splash, but none disappears.
In practice
A bouncing ball never bounces back to the same height because some energy spreads out as heat and sound.
Practice
Flashcards
- What does the law of conservation of energy say?Energy cannot be made or destroyed, only moved between stores or spread out.
Interview questions
- Explain why a bouncing ball does not return to its original height.
- The ball has gravitational energy at the top
- Some energy becomes thermal and sound on impact
- Total energy is conserved but not all stays useful
- So the next bounce has less kinetic energy
Questions people ask
If energy is never lost, why do things run out of energy?
Energy is not destroyed, but it spreads out into the surroundings as heat, which is hard to use again. A battery runs flat because its chemical store has been moved on, ending up as warmed air and parts. Useful energy is used up, even though total energy stays the same.
Where does the energy go when a ball stops bouncing?
It ends up as thermal energy in the ball, the floor and the air, plus a little sound. Each bounce wastes some energy as heat. The total amount of energy stays constant, but it is spread out so widely that it cannot make the ball move again.