# A weather balloon is filled with gas at ground level. As the balloon rises to high altitude, the temperature of the gas drops significantly. Explain, in terms of gas particles, why the pressure of the gas inside the balloon decreases as the temperature falls. Assume the volume of the balloon stays constant.

> Eduqas GCSE Physics — 2.2 The kinetic theory and gas pressure · Explain · 4 marks

> Weather balloons carry instruments into the upper atmosphere, where temperatures can be extremely low.

## Mark scheme (4 marks)

1. Decreasing temperature means the gas particles have less kinetic energy / move more slowly
2. Particles collide with the walls of the balloon less frequently
3. Each individual collision exerts less force on the walls because the particles are moving more slowly
4. Pressure is the perpendicular force per unit area on the container walls, so with less frequent and less forceful collisions, the pressure decreases

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE 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-weather-balloon-is-filled-with-652eb1df) · Published by Druglandscape Ltd.