Describe the types of Pressure and how to mesure.

Pressure  - Pressure is defined as the force applied perpendicular to an object per unit area. mathematically pressure is expressed as -

$P = \frac{F}{A}$

where , 

• F is the force  applied perpendicularly.
• A is the area of the application of force.

- The unit of the force is Pascals (N/m²)

- The most common example of pressure is the atmospheric pressure that is exerted by the atmosphere on different objects on the earths surface.

Types of pressure  - 

1 -Absolute pressure  - 

• The pressure measured with reference to absolute vacuum is termed as the absolute pressure.
• Absolute pressure can never be negative.

2- Gauge pressure - 

• The pressure measured relative to the atmospheric pressure at a given location is called the gauge pressure.
• Gauge pressure can be positive or negative .
• Gauge pressure measured above the atmospheric pressure is positive gauge pressure and that measured below the atmospheric pressure is negative gauge pressure also called as "vacuum pressure".

general formula relating the two pressure is -

Absolute pressure  = Atmospheric pressure $\pm$ gauge pressure.

3-Differential pressure -

• The pressure measured as a difference of pressure at two locations , for example - between two sections of a pipe carrying a fluid, is called the differential pressure.