Pressure (Years 8–11) — Science

Press the flat of your hand against a drawing pin and nothing happens. Press the point and it pushes straight into the board. Same push, wildly different result — because pressure is about how that force is concentrated.

Why this matters: Pressure explains why knives are sharp, why camels and snowshoes have wide feet, and why a stiletto heel can dent a wooden floor that an elephant would not. Master one small equation and all of it clicks into place.

Same force, different area — very different pressure

What pressure means

Pressure is how much force presses on each unit of area. Spread a force over a big area and the pressure is low; squeeze the same force onto a tiny area and the pressure becomes huge. The force has not changed — only how it is shared out.

Pressure = force ÷ area
Force is in newtons (N), area in square metres (m²), so pressure comes out in pascals (Pa), where 1 Pa = 1 N/m².

Cover what you want: P = force ÷ A.

An analogy

Same weight: snowshoes spread the force, lowering the pressure.

Imagine standing on fresh snow. In boots you sink; in snowshoes you stay on top. Your weight (the force) is identical — but snowshoes spread it over a much larger area, so the pressure on the snow drops below what would break the surface. A sharp knife does the opposite: it channels your pushing force onto a razor-thin edge, so the pressure at that edge is enormous and it slices through.

Big area or small area?

A sharp edge squeezes the same force onto a tiny area — high pressure.

Aim	Area needed	Everyday example
High pressure (to cut or pierce)	Small	Knife edge, drawing pin, nail
Low pressure (to avoid sinking or damage)	Large	Snowshoes, wide tyres, camel feet

So a smaller area gives a higher pressure, and a larger area gives a lower pressure — for the very same force.

Worked reasoning

Worked example. A force of 20 N acts on an area of 4 m². Find the pressure.
Ask: "how much force is pushing on each single square metre?" That is force ÷ area.
Pressure = 20 ÷ 4 = 5 Pa (which is 5 N/m²).
Check the units make sense: newtons divided by square metres gives N/m², exactly what a pascal is.

Common mix-up: Multiplying force by area instead of dividing. Remember it is force ÷ area — a larger area should give a smaller pressure, so area must be on the bottom. If your answer gets bigger when the area grows, you have flipped it.

Memory hook: think of a PFA triangle — Pressure on top, Force and Area below: P = F ÷ A.