# A pendulum bob is pulled to one side and released. It swings down to the lowest point of its path and continues upward to the other side. Explain the energy transfers that occur from the moment the bob is released until it reaches the highest point on the other side, and explain why the bob does not rise to exactly the same height as the starting position.

> Edexcel GCSE Physics (1PH0) — 3.1 Conservation of energy · Explain · 4 marks

> A pendulum consists of a small metal bob attached to a string. The bob is pulled to one side, raising it above its lowest position, and then released from rest.

## Mark scheme (4 marks)

1. As the bob swings downward, gravitational potential energy (GPE) is transferred to kinetic energy (KE).
2. As the bob swings upward on the other side, kinetic energy (KE) is transferred back to gravitational potential energy (GPE).
3. Some energy is transferred to the surroundings as heat (and sound) due to air resistance / friction at the pivot — this is a waste energy transfer.
4. Because energy has been dissipated to the surroundings, less GPE is stored at the top of the other side, so the bob does not reach the original height — total energy in the system has decreased.

## Related

- [Revision notes for Edexcel GCSE Physics (1PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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