# A student leaves a fully inflated balloon on a windowsill in a warm room. Later, after the room has cooled overnight, the student notices the balloon has shrunk in size. The amount of gas inside the balloon has not changed. Explain, using kinetic theory, why the balloon shrinks when the temperature decreases.

> Eduqas A-Level Physics — 3.3 Kinetic theory · Explain · 5 marks

## Mark scheme (5 marks)

1. The gas particles move more slowly when temperature decreases
2. The particles hit the walls of the balloon less frequently
3. Each collision exerts a smaller force on the balloon wall
4. The pressure exerted by the gas on the inside of the balloon decreases
5. The lower internal gas pressure is less able to resist the elastic force of the balloon material, so the balloon contracts / volume decreases

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](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-student-leaves-a-fully-inflated-c29b5d17) · Published by Druglandscape Ltd.