Pressure

When a force is applied to a solid object such as a drawing pin or a nail, the force is transmitted through the solid. Factors that determine the effect of the force in cutting or piercing include:

• the size of the force
• the area of contact.

These two factors together are used to calculate the pressure.

Pressure = normal force per unit area
p = F/A
Pressure is measured in pascal (Pa) where 1 Pa = 1 N m^–2

If the force that causes the pressure is not acting in a direction normal to the surface, then the normal component of the force is used to calculate the pressure.

Whereas a solid transmits a force in the direction in which it is applied, fluids (liquids and gases) transmit pressure. The pressure at any point in a fluid has the same value in all directions. The transmission of pressure by a fluid is used in hydraulic machinery, where the force exerted by the fluid is determined by its pressure and the area over which it acts. This enables a large force to be exerted by the application of a small force that causes the pressure in the fluid. The principle of a hydraulic lifting device is shown in the diagram.

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