# A physics teacher places a ping-pong ball on the surface of water in a ripple tank. The teacher then switches on the oscillating paddle to produce water waves. Explain why the ping-pong ball does not travel across the tank in the direction the waves are moving, and describe what the ping-pong ball does instead.

> OCR A-Level Physics A (H556) — 5.1 Thermal physics · Explain · 5 marks

> A ripple tank is a shallow glass tank of water. An oscillating paddle produces regular water waves that travel across the surface. A ping-pong ball is floating on the water's surface when the waves are switched on.

## Mark scheme (5 marks)

1. The ping-pong ball (particle) does not travel in the direction of wave travel because it is the wave/energy that travels, not the medium/water itself.
2. Water waves are transverse waves, meaning particle oscillations are perpendicular to the direction of energy transfer.
3. The ping-pong ball moves up and down (vertically) as the wave passes.
4. The ball oscillates between crests and troughs — moving up to the crest and down to the trough — with a displacement equal to the amplitude of the wave.
5. This provides evidence that a wave transfers energy without transferring matter/the medium.

## Key terms

- [wave](https://www.gradenine.co.uk/glossary/wave)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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-physics-teacher-places-a-ping-pong-986d7411) · Published by Druglandscape Ltd.