Pressure
Year 8 🚀 Forces & Motion Calculate pressure in solids and liquids: P = F/A.
🎯 What is Pressure?
Pressure is the force per unit area. A small force on a tiny area creates a very high pressure — that's why needles and knife edges are so sharp!
⚡ Pressure Formula
$$P = \frac{F}{A}$$
$P$ = pressure (Pa or N/m²) · $F$ = force (N) · $A$ = area (m²)
🦶 Example: A 600 N person stands on one foot (area 0.03 m²).
P = 600 ÷ 0.03 = 20,000 Pa. On both feet: P = 600 ÷ 0.06 = 10,000 Pa — half the pressure!
P = 600 ÷ 0.03 = 20,000 Pa. On both feet: P = 600 ÷ 0.06 = 10,000 Pa — half the pressure!
💡 Pressure Applications
Understanding pressure explains many everyday situations.
| 📍 Situation | 🔍 Why? |
|---|---|
| 👠 High heels cause pain | Small area → very high pressure on floor and feet |
| 🐪 Camels have wide feet | Large area → less pressure, don't sink in sand |
| 🔪 Sharp knives cut easily | Very small area → huge pressure at the edge |
| 🎿 Skis on snow | Wide area spreads weight → low pressure, float on snow |
| 🏗️ Building foundations | Wide foundations spread building's weight over large area |
💧 Pressure in Liquids
Pressure in a liquid increases with depth and acts in all directions.
💧 Liquid Pressure
$$P = \rho g h$$
$\rho$ = density (kg/m³) · $g$ = 10 N/kg · $h$ = depth (m)
🌊 Example: Water density = 1000 kg/m³. At 5 m depth: P = 1000 × 10 × 5 = 50,000 Pa. Twice as deep → twice the pressure!
That's why deep-sea submarines need very thick walls — the water pressure at the ocean floor is about 600 times atmospheric pressure!
Ready to test yourself? Click the Quiz tab above to answer questions on this topic!
🎯 Pressure Calculator (P = F/A)