# A sealed syringe contains a fixed mass of gas at room temperature. The plunger is slowly pushed inward, reducing the volume of the gas. Explain why the pressure of the gas increases as the volume decreases.

> AQA GCSE Physics (8463) — 4.3.3 Particle model and pressure (Phys only) · Explain · 4 marks

> A student pushes the plunger of a sealed syringe inward at a slow, steady rate so that the temperature of the gas inside remains constant.

## Mark scheme (4 marks)

1. The gas molecules are in constant random motion and collide with the walls of the syringe
2. Reducing the volume means the molecules have less space / the molecules are closer together
3. The molecules collide with the walls more frequently / there are more collisions per unit area per second
4. The greater number of collisions per unit area means a greater force per unit area acts on the walls, so pressure increases

## Key terms

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

## Related

- [Revision notes for AQA GCSE Physics (8463)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-sealed-syringe-contains-a-fixed-d8748f4c) · Published by Druglandscape Ltd.