Pressure

• Pressure = force per unit area: P = F/A.
• Why sharp knives, drawing pins, and stiletto heels behave differently from blunt objects.
• How broad camel feet, wide bag straps, and tractor tyres reduce pressure.
• SI unit pascal (Pa) = N/m².

1. Formula — Pressure P = F/A; same force on smaller area → higher pressure.
2. Units — pascal (Pa), also N/cm² in daily use; 1 Pa = 1 N/m².
3. Solids — pressure at contact surface (standing on one foot vs two feet).
4. Liquids — pressure increases with depth: P = hρg (intro level).
5. Diagram (text) — compare knife edge (small A) vs hammer face (large A) for same force.
6. Real world — snow shoes, heavy trucks with many wheels, injection needles.

Finding pressure when a 600 N student stands on one foot (area 0.015 m²)

Given: F = 600 N, A = 0.015 m²
Step 1 — Write P = F/A
Step 2 — P = 600 / 0.015 = 40000 Pa
Step 3 — On two feet (total area 0.03 m²): P = 600/0.03 = 20000 Pa (half)
Step 4 — Smaller area → higher pressure on single foot.

• Using force instead of pressure in explanations (need area too).
• Misconception: heavier person always creates higher pressure (depends on contact area).
• Confusing pressure with force units (Pa vs N).
• Doubling area while doubling force — pressure unchanged (P = 2F/2A = F/A).

• State the formula for pressure with units.
• Why do tractors have broad tyres?
• Force 80 N on 0.02 m². Find pressure in Pa.

Open the Practice tab for graded questions on Pressure.