Simulation liquid pressure
Liquid Pressure Simulation — P = ρgh AQA GCSE Physics | Forces & Pressure
This simulation lets students explore how pressure in a liquid depends on two variables: the depth of the liquid column above a point, and the density of the liquid. It directly addresses the AQA GCSE specification requirement that students explain why pressure increases with both column height and liquid density.
What the simulation shows
The central visual is a tall tank filled with liquid, viewed in cross-section. A probe point sits on the wall of the tank — students can drag it up or down to change the depth, or use the slider in the control panel. As they do, four inward-pointing pressure arrows grow or shrink around the probe, showing that pressure acts equally from all directions at any point in a fluid. This directly illustrates Pascal’s principle without requiring students to be told it.
In the top-right corner, the formula P = ρgh updates live with the actual numbers filled in, and the pressure result is displayed in Pa or kPa. A dial gauge below reflects the same value visually. The left side of the tank shows a double-headed h arrow tracking the depth from surface to probe, so students can see precisely what h represents in the formula.
Students can switch between four liquids — water (1,000 kg/m³), seawater (1,025 kg/m³), oil (800 kg/m³), and mercury (13,600 kg/m³). Switching to mercury at the same depth makes the pressure arrows jump to roughly 13.6 times their water size, giving an immediate visceral sense of how dramatically density affects pressure. The particle density inside the liquid also scales visually — mercury appears packed and dense, oil appears sparse — connecting the abstract number to a physical picture of what density means.
Classroom Activity: Two Variables, One Formula
Objective: Students isolate and investigate the two variables in P = ρgh — depth and density — before combining them to make predictions.
Part 1 — Depth investigation (8 minutes)
Set the liquid to water and ask students to drag the probe to six different depths: 0.5 m, 1.0 m, 1.5 m, 2.0 m, 3.0 m, and 5.0 m. They should record h and P each time in a table.
Ask them to spot the pattern: when depth doubles, what happens to pressure? Students should find that P is directly proportional to h — the relationship is linear. They can plot P against h on paper or a quick graph in their books and draw a straight line through the origin. This confirms the P ∝ h relationship embedded in the formula.
Key question: Why does deeper mean higher pressure? Lead students to reason that more liquid sits above the probe — more mass, more weight, more force per unit area pressing down.
Part 2 — Density investigation (8 minutes)
Fix the depth at 2.0 m. Ask students to switch between all four liquids and record ρ and P each time.
They should observe that the ratio P/h stays constant for a given liquid (equal to ρg), and that switching from oil to mercury increases pressure by a factor of 17. Ask students to calculate the expected pressure for each liquid using P = ρgh before checking their answer in the simulation.
Key question: Why does denser liquid produce more pressure at the same depth? Guide students toward the idea that denser liquid has more mass per cubic metre — so the column of liquid above the probe is heavier even though it is the same height.
Part 3 — Prediction challenge (5 minutes)
Pose this problem without the simulation: A diver descends 10 m into seawater (ρ = 1 025 kg/m³). What is the pressure from the water alone at that depth?
Students calculate: P = 1025 × 9.8 × 10 = 100,450 Pa ≈ 100.5 kPa. Then ask them to compare this to the pressure at the same depth in fresh water (1000 × 9.8 × 10 = 98,000 Pa). The difference — about 2.5 kPa — comes entirely from the higher density of seawater.
Follow-up discussion: Why do deep-sea vehicles need to be built so strongly? What would happen to a submarine if it went twice as deep?
SEND notes: The accessibility panel offers high contrast, large text, dyslexia-friendly spacing, and reduced motion (which pauses the particle animation for students who find movement distracting). The drag-and-drop probe gives a physical, tactile way to explore depth that may suit kinaesthetic learners better than typing numbers or reading off a graph.