Pressure

Beginner

Force per unit area.

Key relationP = F/A

P = F/A: force per unit area acting perpendicular to a surface. The same force on a smaller area gives a larger pressure; that's why knives cut.

Worked example

A 60 kg person on 0.02 m² of shoes: 29 kPa; on snow shoes of 0.4 m²: 1.5 kPa.

Common mistake

Pressure is a scalar, force is a vector.

In more detail

Pressure is force per unit area, P = F/A. In a fluid, pressure acts equally in all directions at a point, and it is measured in pascals.

Tyre pressure keeps vehicles safe and efficient.
Weather forecasts track atmospheric pressure changes.
A sharp knife cuts better than a blunt one because the same force acts over a smaller area, producing a larger pressure.

What is the SI unit of pressure?

The pascal, equal to one newton per square metre.

Why does a sharp knife cut better?

Because the same force acts over a smaller area, giving higher pressure.

Why do snowshoes help walkers?

They spread the body's weight over a larger area, which reduces the pressure on the snow.