Pascal's Principle

• also known as Pascal's principle of transmission of pressure in fluids.
• the principle was established by French mathematician Blaise Pascal.
• states that pressure exerted on an enclosed fluid (liquid) is transmitted equally to every part of the fluid (liquid).
• This principle is stated mathematically as:

  

  where

   = hydrostatic pressure (Pa)

            ρ = fluid density (kg m^-3) 

            g = acceleration due to gravity (m s^-2)

    = height of fluid above the point of measurement (m) 

Idea of Transmission of Pressure in a Liquid

                                        

            The effects of Pascal's law, as Pascal discovered in his 1646 barrel experiment

• 2 properties of liquid made use in hydraulic system :  

          a) it is incompressible                                                                                                                                                                                                                                      b)if a pressure is applied to an enclosed liquid, then the pressure would be transmitted to all parts of it 

• when the piston is pushed inwards, water is compressed by the applied force.
• the force of compression per unit surface area gives rise to pressure exerted on the water.
• since the volume of a liquid is constant, the pressure applied is transmitted equally in all directions throughout the liquid thus proving Pascal's principle.

Simple Hydraulic System

• consists of 2 cylinders with each cylinder is fitted with a piston and filled with a liquid such as water and oil.
• when a small force, F1 is applied to the smaller piston X, a large force, F2 is produced on the larger piston Y.
• F2 is produced by pressure exerting on the larger piston Y due to the pressure transmitted from piston X through the liquid.
• if there are some air bubbles present in the hydraulic fluid, the hydraulic system will not operate fully because the force applied on the small piston is partly used to compress the air bubbles and not fully used to exert a pressure on the large piston.