# What is (Mechanical) Pressure?

Level 2 (without higher mathematics)
Level 2 requires school mathematics. Suitable for pupils.
Updated by Alexander Fufaev on

The pressure $$\mathit{\Pi}$$ is defined as the force $$F$$ acting perpendicularly on a surface area $$A$$:

Formula anchor

The pressure is abbreviated here with the Greek capital letter $$\mathit{\Pi}$$ (pronounced: Pi). Sometimes the pressure is also abbreviated with the letter $$p$$, but that is avoided here because $$p$$ is already used for the momentum.

Pressure unit:
The force $$F$$ has the unit $$\mathrm{N}$$ (newtons) and stands for the unit $$\frac{\mathrm{kg} \, \mathrm{m}}{\mathrm{s}^2}$$ (kilograms per second squared). The area $$A$$ has the unit $$\mathrm{m}^2$$ (square meter). Because of equation 1 the pressure $$\mathit{\Pi}$$ must have the unit $$\frac{\mathrm{N}}{\mathrm{m}^2}$$. Newton per square meter is usually abbreviated with the unit $$\mathrm{Pa}$$ (Pascal) for pressure.

From the definition 1 of pressure, we can read the following information:

• The larger the force $$F$$, the larger the pressure $$\mathit{\Pi}$$.

• The smaller the surface $$A$$ on which the force is applied, the greater the pressure $$\mathit{\Pi}$$.

There are several special names of pressure, but they can all be traced back to the definition 1. Here are some examples:

• Air pressure - is caused by the gravitational force exerted by the air. The air pressure at sea level is $$10^5 \, \mathrm{Pa}$$. Therefore, the unit "bar" is usually used for air pressure: $$1\, \mathrm{bar} = 10^5 \, \mathrm{Pa}$$.

• Gravity pressure - is also caused by the gravitational force exerted by a liquid or gas.