# Explain why the upthrust acting on a submarine increases as it dives deeper into the ocean.

> AQA GCSE Physics (8463) — 4.5.5 Pressure and pressure differences in fluids (Phys only) · Explain · 4 marks

> A submarine dives from the surface of the ocean to a greater depth. As it descends, the crew notice that the ballast tanks must be adjusted to maintain a steady depth.

## Mark scheme (4 marks)

1. Pressure in a fluid increases with depth
2. The pressure difference between the bottom and the top of the submarine increases (as the submarine dives deeper)
3. This greater pressure difference produces a larger net upward force on the submarine
4. Upthrust equals the weight of fluid displaced, and at greater depth the submarine displaces the same volume but the surrounding fluid exerts more pressure, giving a greater upthrust

## Key terms

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

## Related

- [Revision notes for AQA GCSE Physics (8463)](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/explain-why-the-upthrust-acting-on-0ec54d6f) · Published by Druglandscape Ltd.