- The definition of pressure
- The formula of pressure (you need this formula to do lot of calculation.)
- The SI unit of pressure
- 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,

$$\begin{array}{l}\text{Pressure}=\frac{\text{Force}}{\text{Area}}\\ P=\frac{F}{A}=\frac{20N}{4c{m}^{2}}=5N/c{m}^{\mathrm{\xb2}}\end{array}$$

### 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.__Magnitude of the force.__

The larger the force, the higher the pressure.__Contact area.__

The larger the contact area, the lower the pressure.