Device used to Measure Pressure in a Fluid

A simple device used to measure pressure in a fluid is shown in figure 1. It consists of an evacuated cylinder. A piston of area A is fitted into the cylinder. A spring is connected between the piston and the bottom of the cylinder. 

When the device is submerged in a fluid, the fluid exerts a force (F) on the piston, As a result of this downward force, the spring is compressed as long as the downward force exerted by the fluid on the piston is equal to the upward force exerted by the spring on the piston. Force exerted by the fluid can be determined by calibrating the compression of the spring with a known force. Therefore, the pressure in a fluid can be determined using the relation, P = F/A.

Pressure is a scalar quantity. A definite direction is not associated with pressure because  hydrostatic pressure is transmitted equally in all directions when force is applied

Units of Pressure

• In the CGS system, the unit of pressure is dyne cm^-2.
• In SI, the unit of pressure is Nm^-2 or Pascal (Pa)
• Dimensional Formula of Pressure is [ ML^-1T^-2 ]
• The unit of pressure, Pascal (Pa) has been named in the honor of a great French Scientist and Philosopher Blaise Pascal.

Liquids and gases play an important role in our life. The earth’s atmosphere is so big as it appears like an ocean of gases. About 76% of the surface of the earth is covered with water. We cannot think of a life without gases (air) and water, Liquids are collectively known as fluids. A substance that flows under the action of an applied force and does not have a shape of its own is known as a liquid. The study of fluids which is at rest is known as hydrostatic or fluid statics. The study of hydrodynamics. In this article, we will have the study of liquids only.