# A sealed syringe contains a fixed amount of air. When the plunger is pushed inward, reducing the volume of the air inside, the pressure of the air increases. Explain, using ideas about particle collisions, why reducing the volume of the air inside the syringe causes the pressure to increase.

> OCR GCSE Physics A: Gateway Science (J249) — P1.3 Pressure · Explain · 4 marks

> A student pushes the plunger of a sealed syringe inward, reducing the volume of the trapped air. The student notices that the syringe becomes harder to push as the plunger moves further in.

## Mark scheme (4 marks)

1. Reducing the volume means the particles are confined to a smaller space / the particles are closer together
2. The particles collide with the walls of the syringe more frequently
3. Each collision exerts a perpendicular force on the wall / the force per unit area on the walls increases
4. More frequent collisions per unit area means greater pressure, because pressure is the force acting perpendicular to a surface per unit area

## Key terms

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

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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-sealed-syringe-contains-a-fixed-3770e5d1) · Published by Druglandscape Ltd.