# A helium weather balloon is released from the Earth's surface and rises high into the atmosphere. Explain why the balloon expands as it rises to a greater altitude.

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

> Weather balloons are used by meteorologists to collect data about the atmosphere. They are filled with helium at the Earth's surface and released to rise through the atmosphere.

## Mark scheme (4 marks)

1. Atmospheric pressure decreases as the balloon rises to a greater altitude
2. There are fewer air molecules above at greater altitude, so the weight of air above is less
3. The pressure of the helium inside the balloon is greater than the atmospheric pressure outside
4. The balloon expands until the pressure inside equals the pressure outside / until equilibrium is reached

## Key terms

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

## 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-helium-weather-balloon-is-released-1e22f1b5) · Published by Druglandscape Ltd.