A fluid is any substance that can flow — this includes both liquids and gases. Pressure in a fluid behaves differently from pressure on a solid surface. There are three key rules:
- Fluids exert pressure in ALL directions — not just downward. A submarine at depth has water pressing in on it from all sides, not just from above.
- Pressure increases with depth — the deeper you go, the greater the weight of fluid above you.
- Pressure at a given depth is the same in all directions at that point.
The formula for pressure due to a column of liquid is:
Where h = depth below the surface, ρ (rho) = density of the liquid, and g = 9.8 N/kg on Earth. This is a Higher equation.
This deep dive covers Pressure in Fluids (Liquids and Gases) within Pressure for GCSE Physics. Revise Pressure in Forces for GCSE Physics with 15 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 3 of 16 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Pressure
What is the correct equation for pressure?
Explain why a sharp knife cuts through food more easily than a blunt knife, even when the same force is applied to both.