Fiducia TogetherPressure and forces in fluids
Force spread over an area, and why it changes with depth and height.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
Pressure is force per unit area, in pascals. In a fluid, pressure increases with depth because of the weight of fluid above, and acts in all directions.
Where it applies
GCSE physics, and parts of it are higher tier only.
How it works
Atmospheric pressure decreases with altitude because there is less atmosphere above. Upthrust arises because pressure is greater at the bottom of a submerged object than at the top, which is why things float.
An object floats when the upthrust equals its weight.
How to use it in your work
Use the correct equation for the context — force over area for a solid, and the depth equation for a fluid column.
Explain floating by comparing upthrust and weight, not by saying something is 'light'.
Check units: area in square metres, and pressure in pascals.
Where to get help
Your teacher, your board's specification for the depth required at your tier, and Bitesize for the diagrams.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Physics Song The GCSE physics specification, set to music.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.