# A bicycle pump contains a fixed mass of air. When the nozzle of the pump is blocked and the handle is pushed in, the volume of the air decreases at constant temperature. Explain why the pressure of the air inside the pump increases.

> Pearson Edexcel International GCSE Physics (4PH1) — 5.3 Ideal gas molecules · Explain · 4 marks

> A cyclist blocks the nozzle of a bicycle pump and pushes the handle inward, compressing the trapped air to a smaller volume. The temperature of the air remains constant throughout.

## Mark scheme (4 marks)

1. The gas molecules collide with the walls of the pump (more frequently / more often)
2. Because the molecules are closer together / the volume is smaller, so they travel a shorter distance between collisions with the walls
3. Each collision exerts a force on the wall (because the molecule changes momentum / direction on rebounding)
4. Greater frequency of collisions means a greater force per unit area / greater pressure on the walls

## Key terms

- [pressure](https://www.gradenine.co.uk/glossary/pressure)
- [volume](https://www.gradenine.co.uk/glossary/volume)
- [constant temperature](https://www.gradenine.co.uk/glossary/constant-temperature)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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-bicycle-pump-contains-a-fixed-ac002353) · Published by Druglandscape Ltd.