Pressure and Force

Pressure tells us how much a force is spread over an area. The same force over a small area gives a large pressure; the same force over a large area gives a small pressure.

Key idea and equation

Pressure is the force acting per unit area, at right angles to a surface.

$$p = \frac{F}{A}$$

Where $p$ is pressure in pascals (Pa), $F$ is force in newtons (N), and $A$ is area in square metres (m²). 1 Pa = 1 N/m². You can rearrange: $F = pA$ and $A = \frac{F}{p}$.

In everyday cases, the force is often the object’s weight (the pull of gravity), measured in newtons.

Everyday examples

• High-heeled shoes press into the ground more than trainers because the heel tip has a smaller area.
• Snowshoes spread your weight over a larger area, so you are less likely to sink.
• A sharp knife cuts better because its thin edge has a very small area, making the pressure larger.
• Lying on a bed of many nails can be safe because your weight is shared over lots of points (large total area).