Conservation of energy
Energy is transferred, never created or destroyed.
The common mistake
Saying energy is 'used up' or 'lost' rather than transferred (often to heat).
Instead: Track where energy goes: total in = total out. 'Wasted' energy is usually heat to the surroundings.
Worked example with Guide me
A 1 kg ball falls 5 m (g = 10). Ignoring air, how much KE does it have at the bottom?
- Sugar · GPE at the top?Student · 1 × 10 × 5 = 50 J.
- Sugar · Where does it go?Student · All into kinetic energy.
Answer: 50 J
Try 3 practice questions
1. A lamp uses 100 J and gives 20 J of light. Where's the rest?
Show answer
80 J, mostly as heat
2. Efficiency of that lamp?
Show answer
20%
3. Energy store in a stretched spring?
Show answer
Elastic potential
Quick answers
- What is the most common mistake with conservation of energy?
- Saying energy is 'used up' or 'lost' rather than transferred (often to heat).
- How do I get conservation of energy right?
- Track where energy goes: total in = total out. 'Wasted' energy is usually heat to the surroundings.
- Can you show a worked example?
- A 1 kg ball falls 5 m (g = 10). Ignoring air, how much KE does it have at the bottom? 50 J
Related concepts
Save this as a miss — practice it before your test
Sugar brings it back for review until it sticks. Free, no card.
Save this as a miss — practice it before your test