# A metal tin contains air at room temperature. The tin is placed in a freezer and left until the air inside cools to a much lower temperature. Explain, using kinetic theory, why the pressure of the air inside the tin decreases when it is cooled.

> WJEC A-Level Physics (Wales) — 3.3 Kinetic theory · Explain · 5 marks

## Mark scheme (5 marks)

1. Air is made up of particles (molecules/atoms) that are in constant random motion
2. Pressure is caused by particles colliding with the walls of the tin
3. When the temperature decreases, the particles move more slowly / have less kinetic energy
4. Slower particles hit the walls with less force
5. Fewer collisions per second with the walls (at lower temperature), so overall pressure is lower

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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-metal-tin-contains-air-at-0efe5156) · Published by Druglandscape Ltd.