# A buoy floating on the surface of the sea bobs up and down in simple harmonic motion as waves pass beneath it. The buoy starts at its maximum displacement above the equilibrium position and is then released. Describe the motion of the buoy over one complete oscillation, including how its speed and displacement change throughout.

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

> A buoy is anchored in open water. Ocean waves cause it to oscillate vertically with a regular time period. At the start of the observation, the buoy is at its maximum displacement above its equilibrium (undisturbed) position.

## Mark scheme (5 marks)

1. At maximum displacement (amplitude) the buoy has zero velocity / is momentarily stationary
2. The buoy accelerates towards the equilibrium position / restoring force acts towards equilibrium
3. The buoy reaches maximum speed as it passes through the equilibrium (undisturbed) position
4. The buoy then decelerates / slows down as it moves towards the maximum displacement below equilibrium
5. The buoy returns to its original position (completing one full oscillation) in a time equal to one time period

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-buoy-floating-on-the-surface-de73974d) · Published by Druglandscape Ltd.