Pascal's Law and Hydraulic Brake System. Pascal's Law Pascal's Law was formulated by Blaze Pascal to describe the effects of pressure within a liquid. The law states that the pressure exerted anywhere in a mass of confined liquid is transmitted undiminished in all directions throughout the liquid. The working of hydraulic devices like the hydraulic press and the hydraulic brakes are based on this principle. The hydraulic brake system. We all know that a car slows down and stops when we apply brakes. But how does this happen? How does the force exerted on the foot pedal stop or slow down a car? How does it multiply the force so that it is enough to stop something as big as a car? The basic idea behind any hydraulic system is very simple. The force applied at one point is transmitted to another point using an incompressible fluid, generally oil. Most brake systems also multiply the force in the process. Here you can see the simplest possible hydraulic system. Two pistons are fitted into two glass cylinders filled with oil and connected to one another with an oil-filled pipe. If you apply a downward force on one of the pistons, then the force is transmitted to the second piston through the oil in the pipe. Since oil is incompressible, the efficiency is very good. Thus most of the applied force appears at the second piston. The advantage of hydraulic systems is that the pipe connecting the two cylinders can be of any length and shape, allowing it to choose any part separating the two pistons. The other advantage about a hydraulic system is that it multiplies the force applied. Here you can see the hydraulic brake system of an automobile. It consists of a pipeline containing fluid, one end of which is connected to the master cylinder fitted with a piston attached to the foot pedal. The other end of the pipeline is connected to the wheel cylinder, having two pistons, P1 and P2, attached to the brake shoes. The area of cross section of the wheel cylinder is greater than the area of the cross section of the master cylinder. Let us see what happens when brakes are applied. When the brakes are applied, the foot pedal is pushed due to which pressure is exerted on the fluid in the master cylinder. This pressure is transmitted equally and undemannished throughout the fluid and to the pistons of the wheel cylinder. Therefore the pistons get pushed outwards and the brake shoes get pressed against the rim of the wheel due to which the motion retarts. On releasing the pressure on the pedal, the return spring forces the pistons of the wheel cylinder back and the fluid flows back into the master cylinder. Hope you will remember this the next time you see a driver applying brakes.