Force experienced per unit area is known as pressure.
Pressure = Force / Area
Units of pressure is Newton / metre2 or N / m2
Example – Liquids and gases exert pressure on the walls of the container.
Absolute pressure (pa): The pressure measured above absolute zero of pressure is called absolute zero pressure. A absolute zero pressure occurs only in complete volume.
Absolute pressure = Gauge pressure + Atmospheric pressure
pa = pg + patm
Gauge pressure (pg): The instrument used to measure the pressure generally measure the difference between the system pressure and atmospheric pressure. This is known as gauge pressure.
Vaccum pressure: It is difference between the atmospheric pressure and absolute pressure.
Vaccum pressure = Atmospheric pressure – absolute pressure
1 atmospheric pressure = 1.01325 bar
The pressure exerted by the surrounding air is known as atmospheric pressure.