# Use the kinetic theory of matter to explain why a gas fills any container it is placed in, but a liquid only fills the bottom of a container.

> WJEC GCSE Physics (Wales) — 1.8 Kinetic theory · Explain · 4 marks

## Mark scheme (4 marks)

1. In a gas, particles move in random directions / randomly in all directions
2. Gas particles have (almost) no forces of attraction between them / negligible intermolecular forces, so they are not held together
3. In a liquid, particles are still attracted to each other / have forces of attraction between them that keep them close together
4. Liquid particles can move/flow/slide past each other but are not free to move far apart / cannot overcome the attractive forces to fill the whole container

## Key terms

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

## Related

- [Revision notes for WJEC GCSE 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/use-the-kinetic-theory-of-matter-e8d111d6) · Published by Druglandscape Ltd.