Transmission of pressure in liquid
Pascal's Law
Pascal's law states that pressure applied to an enclosed liquid, is transmitted equally to every part of the liquid.
This can de demonstrated using a glass vessel as shown in figure above. When force is applied to the piston the pressure exerted on the water is transmitted equally throughout the water so that water comes out of all the holes with equal force.
When pressure is applied at a point in a confined fluid, it is transmitted equally in all directions.
Hydraulic devices like hydraulic press and car brakes are based on the above principle.
This system of braking is shown in figure above. The brake shoes are expanded by a cylinder having two opposed pistons. These are forced outwards by liquid under pressure conveyed by a pipe from the master cylinder. The piston of the master cylinder is worked by the brake pedal. When pressure on pedal is released, the brake shoe pull-off springs force the wheel pistons back into the cylinders and the liquid is returned to the master cylinder. A very important advantage of this system is that the pressure set up in the master cylinder is transmitted equally to all four wheel cylinders so that the braking effort is equal on all the wheels.
