What is Pascal’s Law and how do we use it?
An external force applied on the surface of a liquid increases the liquid pressure at the surface of the liquid. This increase in liquid pressure in transmitted equally in all directions and to the walls of the container in which it is filled. This result is called Pascal’s law which is stated:
“ Pressure applied at any point of a liquid enclosed in a container, is transmitted without loss to all other parts of the liquid”.
It can be demonstrated with the help of the glass vessel having holes all over its surface. Fill it with water. Push the piston. The water rushes out of the holes in the vessel with the same pressure. The force applied on the piston exerts pressure on water. This pressure is transmitted equally throughout the liquid in all directions.
In general, this law holds good for fluids both for liquids as well as gases.
Applications of Pascal’s Law in real life
Pascal’s law finds numerous applications in our daily life such as automobiles, hydraulic brake system, hydraulic jack, hydraulic press and other hydraulic machines.
Pascal law and its applications in Hydraulics
Hydraulic press is a machine which works on Pascal’s law. It consists of two cylinders of different cross-sectional areas. They are fitted with pistons of cross-sectional areas a and A. The object to be compressed is placed over the piston of large cross-sectional area A. The force F1 is applied on the piston of small cross-sectional area a. The pressure P produced by small piston transmitted equally to large piston and a force F2 acts on A which is much larger than F1.
Press on piston of small area a is given by :
Apply pascal’s law, the pressure on large piston of area A will be the same as on small piston.
- P =F2/A
Comparing the above equations, we get:
F2= A ×F1/a
F2 = F1 ×A/a
Since the ratio is greater than 1, hence the force F2 that acts on the larger piston is greater than the force F1 acting on the smaller piston. Hydraulic systems working in this way are known as force multipliers.
The braking systems of cars, buses, etc.also work on pascal’s law. The hydraulic brakes allow equal pressure to be transmitted throughout the liquid. When brake pedal is pushed, it exerts a force on the master cylinder, which increases the liquid pressure in it. The liquid pressure is transmitted equally through the liquid in the metal pipes to all the pistons of the other cylinders. Due to the increase in liquid pressure, the pistons in the cylinders move outward pressing the brake pads with the brake drums. The force of friction between the brake pads and the brake drums stops the wheels.