The formula
P = F / A
| Symbol | Quantity | Unit |
|---|---|---|
| P | Pressure | Pa |
| F | Force | N |
| A | Area | m² |
What it means
Pressure measures how concentrated a force is. Push with the same force through a needle and through your palm and the effects differ entirely, because the area differs by orders of magnitude.
How to work it out by hand
- Take the force in newtons
- Divide by the area in square metres
- The answer is in pascals
What is worth knowing
A pascal is a very small unit — one newton over a square metre — which is why weather uses hectopascals and tyres use bars. Atmospheric pressure at sea level is about 101,325 Pa, which works out at roughly ten tonnes pressing on an average person; we do not feel it because the same pressure acts inside us. The drawing-pin principle runs both ways: snowshoes and tank tracks spread a load to reduce pressure, while knives and nails concentrate it. The force is unchanged in both cases; only the area moves.