Understanding Pressure

In SPM, you need to know

1. The definition of pressure
2. The formula of pressure (you need this formula to do lot of calculation.)
3. The SI unit of pressure
4. Factors affecting the magnitude of pressure

Pressure

Pressure is defined as the force acting normally per unit area. (Here, the word "normally" means perpendicularly.)

   

Example

As shown in the diagram above, a 20N force acts on a 4cm² surface. The force is shared equally by the surface, hence each 1 cm² of the surface withstand a force of 5N (20N/4).

The force (5N) acts on 1 unit area (1cm²) is said to be the pressure acting on the surface. Therefore, the pressure acting on the surface is 5N/cm².

Mathematically,
$$\begin{array}{l}\text{Pressure}=\frac{\text{Force}}{\text{Area}}\\ P=\frac{F}{A}=\frac{20N}{4c{m}^2}=5N/c{m}^{\mathrm{²}}\end{array}$$

Unit of Pressure

The SI unit of pressure is Pascal (Pa). 1 Pa is equal to1 newton per metre2 (N/m²).

1 N/m² = 1 Pa

Factors Affecting the Magnitude of Pressure

Factors that affect the pressure acting on a surface.

1. Magnitude of the force.
   The larger the force, the higher the pressure.
2. Contact area.
   The larger the contact area, the lower the pressure.