Pressure in a fluid 1 — AQA GCSE Physics
Test yourself on Pressure in a fluid 1 with AQA GCSE practice questions.
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Pressure in a fluid 1 explained
A fluid is anything that flows, which covers both liquids and gases and excludes solids.
Read the full explanation
In a solid the particles are held in fixed positions and can only vibrate, so a solid keeps its shape. In a liquid the particles touch but slide past one another, so a liquid takes the shape of its container while keeping its volume. In a gas the particles are far apart and move randomly at speed, so a gas fills whatever space it is given. Because their particles can move, both liquids and gases press outwards on every surface they touch, and both can be pumped along a pipe. The differences matter too: a gas can be compressed because of the space between its particles, and its density is far lower, which is why pressure changes with depth much faster in water than in air.
Your focus
- Classify given substances as fluids or not, and justify each choice.
- Describe the particle arrangement in a liquid and in a gas that allows both to flow.
- Explain why a gas can be compressed but a liquid can barely be.
Pressure in a fluid 1 exam tips
Marking Points
- one mark for a fluid identified as a substance that can flow
- one mark for both liquids and gases counted as fluids
- one mark for a particle arrangement that allows the particles to move past one another
- one mark for stating that a fluid exerts pressure on every surface it touches
Examiner Tips
- 💡If a question says fluid, check whether the substance in the figure is a gas; the same equations still apply.
- 💡Use the word flow in any definition, because that is what is being tested.
Common Mistakes
- restricting the word fluid to liquids only
- saying a gas has no mass or exerts no pressure
- describing the particles in a liquid as far apart, which is the arrangement in a gas
- claiming a liquid can be compressed as easily as a gas