A tennis ball is dropped from rest and falls vertically downwards onto a hard floor. The ball bounces back upwards but does not reach its original height. Explain why the ball does not return to its original height after bouncing.

Edexcel GCSE Physics (1PH0) — 8.1 Energy — forces doing work · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A tennis ball is dropped from rest and falls vertically downwards onto a hard floor. The ball bounces back upwards but does not reach its original height.

Model answer (4 marks)

As the ball falls, its gravitational potential energy is converted into kinetic energy.
When it strikes the floor, work is done against resistive forces such as the deformation of the ball and floor.
During this process some of the energy is dissipated as heat and sound.
Because energy is lost, the ball leaves the floor with less kinetic energy and therefore cannot reach its original height.

Examiner tips

  • Use the word ‘converted’ or ‘transferred’ to link potential and kinetic energy. Mention resistive forces and energy dissipation. Show the causal chain: fall → work → loss → lower height.
  • common_mistakes
  • :
  • Saying the ball simply ‘loses energy’ without specifying heat/sound. Forgetting to mention the resistive forces during impact.

Mark scheme (4 marks)

  1. As the ball falls, gravitational potential energy is transferred to kinetic energy
  2. When the ball hits the floor, work is done against resistive forces (e.g. during deformation / compression of the ball or floor)
  3. Some energy is dissipated (transferred to the surroundings as heat/sound) during the bounce
  4. Because energy has been dissipated, the ball has less kinetic energy after the bounce, so it cannot rise to the same height / regain the same gravitational potential energy

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