A ball is dropped from a height and bounces on the floor several times before coming to rest. Explain, using the idea of conservation of energy, why the ball does not return to its original height after each bounce.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Energy is conserved, so the total energy of the ball–floor system remains constant. When the ball hits the floor, part of its kinetic energy is converted into other forms such as heat and sound, so it is lost from the ball’s mechanical energy.
After each bounce the ball therefore has less gravitational potential energy (and kinetic energy) than it had before the impact. Because the ball now possesses insufficient energy, it cannot climb back up to its original height.
Thus the ball never returns to the same height after each bounce.
After each bounce the ball therefore has less gravitational potential energy (and kinetic energy) than it had before the impact. Because the ball now possesses insufficient energy, it cannot climb back up to its original height.
Thus the ball never returns to the same height after each bounce.
Examiner tips
- Use the phrase ‘energy is conserved’ to show understanding of conservation of energy.
- Explain that energy is lost as heat/sound during the impact.
- Show that the ball’s mechanical energy after the bounce is lower, so the maximum height is lower.
- Keep the answer concise and use the exact wording from the mark scheme.
Common mistakes
- Saying the ball simply ‘loses energy’ without linking it to heat or sound.
- Confusing the ball’s kinetic energy with its potential energy after the bounce.
- Writing a long narrative instead of a short, point‑by‑point explanation.
Mark scheme (4 marks)
- Energy cannot be created or destroyed (conservation of energy)
- Some of the ball's energy is dissipated / transferred as thermal energy or sound energy during each bounce
- The ball has less (gravitational potential / kinetic) energy available after each bounce than it had before
- Therefore the ball cannot rise to the same height because it has insufficient energy to do so
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →