# A child sits on a swing in a playground. The swing is pulled back and released, and the child oscillates back and forth in simple harmonic motion. Explain what is meant by simple harmonic motion and describe how the amplitude and time period of the swing's oscillation change over time as air resistance acts on the system.

> WJEC A-Level Physics (Wales) — 5.1 Simple harmonic motion · Explain · 5 marks

## Mark scheme (5 marks)

1. Simple harmonic motion involves an oscillating object moving repeatedly through an equilibrium (undisturbed) position
2. The restoring force always acts towards the equilibrium position
3. The amplitude decreases over time due to air resistance
4. The time period remains (approximately) constant / does not change as amplitude decreases
5. Energy is transferred from the system to the surroundings (as heat/thermal energy), reducing the total energy of the oscillation

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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/a-child-sits-on-a-swing-daee2925) · Published by Druglandscape Ltd.