GCSE Physics · Edexcel 1PH0 · Topic 15B
Pressure in fluids
Key points
- Pressure is force per unit area: , in pascals (Pa), where 1 Pa = 1 N/m². The force acts at right angles to a surface.
- Pressure in a liquid increases with depth and with the density of the liquid: .
- Atmospheric pressure comes from air particles colliding with surfaces; it decreases with height because there is less air above.
- Upthrust is the upward force from a fluid. It equals the weight of fluid displaced.
- An object floats if its weight is less than or equal to the maximum upthrust it can get, so less dense objects float.
- Divers and submarines need strong hulls because the pressure at great depth is very large.
Topic notesPremium
Liquids and gases (fluids) push on every surface they touch. This sub-topic explains what pressure is, why it increases as you go deeper, and how the difference in pressure on the top and bottom of an object produces upthrust.
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