# Explain why a simple pendulum swinging with a small amplitude is described as undergoing simple harmonic motion.

> AQA A-Level Physics (7408) — 3.6.1 Periodic Motion · Explain · 5 marks

> A simple pendulum consists of a small bob suspended on a light string. When displaced slightly from its rest position and released, the bob oscillates back and forth.

## Mark scheme (5 marks)

1. There is a restoring force acting on the bob
2. The restoring force is directed towards the equilibrium/rest position
3. The magnitude of the restoring force is proportional to the displacement from the equilibrium position
4. The acceleration of the bob is proportional to its displacement from the equilibrium position
5. The acceleration (and restoring force) is always directed towards the equilibrium position, i.e. opposite to the displacement

## Key terms

- [simple harmonic motion](https://www.gradenine.co.uk/glossary/simple-harmonic-motion)
- [amplitude](https://www.gradenine.co.uk/glossary/amplitude)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-simple-pendulum-swinging-b14223e1) · Published by Druglandscape Ltd.