# A sealed bag of crisps is packed at sea level and then taken to the top of a high mountain. Explain why the bag appears more inflated at the top of the mountain than it did at sea level.

> OCR GCSE Physics A: Gateway Science (J249) — P1.1 The particle model · Explain · 4 marks

> A hiker notices that a sealed bag of crisps, which felt firm at sea level, feels puffy and expanded when she reaches the summit of a high mountain.

## Mark scheme (4 marks)

1. Atmospheric pressure decreases with increasing altitude / at the top of the mountain atmospheric pressure is lower than at sea level
2. There are fewer air molecules above the hiker at greater altitude, so the weight of air above is smaller
3. The pressure of the gas inside the bag remains the same / the gas inside the bag exerts a greater force outward than the air outside pushes inward
4. The greater pressure inside than outside causes the bag to expand / inflate

## 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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