Fluid Pressure Definition

Pressure

In engineering, we often encounter with the term pressure especially, when we talk about gases or liquid. Going through the definition of pressure, it is defined as “the normal force exerted by fluid per unit area is called pressure” while in solids, the term pressure is replaced by term “stress”.

                                   

In simple term pressure can be understood as:

Whenever a force comes in contact with a surface, the whole force gets transmitted from one body to another body through this contact surface only. So, the amount of force passing through unit surface area is called pressure.

For example

Suppose a man, weighing 100kg is standing with his both feet on the ground. It is assumed that one foot covers 50 cm² (=.005m²) on the ground. The weight of the man is being transmitted into ground from both feet.

Units of pressure:

The basic SI unit of pressure is pascal (N/m² = Pa). Pascal is very small unit for practical applications. In practice the pressure is of the order of kilo pascal and mega pascal.

1 kilo Pascal = 10³ pa.

1 mega pascal = 10⁶pa.

Other units of pressure

When the pressure is written in comparison with the atmospheric pressure. The unit used is atm.

The atmospheric pressure is measured with the help of barometer.

Its value is,

101325 Pa = 1.01325 x 10⁵Pa = 1 atm.  

Three other pressure units commonly used in practice, especially in Europe, are bar, kilogram-force per square centimeter and pound force per square inch (or Psi).

1 bar = 10⁵Pa = 0.1MPa = 100KPa

1 kgf/cm² = 9.807 N/cm² = 9.807 x 10⁴ N/m² = 0.9807 bar = 0.9679 atm.

1 atm = 14.696 lbf/in² or Psi