How a break system works

A brake is a device used for stopping moving vehicle.
The hydraulic brake is an arrangement which uses break fluid containing ethylene glycol to transfer pressure from the master cylinder to the slave cylinders at each wheel.
Car brakes use the hydraulic principle to to transmit pressure from the foot pedal to the brake. The foot brake of a car operates like a hydraulic press. The movement of the foot pedal operates a piston in the master cylinder and a hydraulic fluid transmits the pressure to slave cylinders which operates the brakes at each wheel. By properly calculating the diameters of the master and slave cylinders, the correct force can be obtained on the brakes of the wheels.
However, it is important in a car braking system that no air should enter the pipe containing the hydraulic fluid. Air unlike liquids, can be compressed, so with air present the brakes will not work properly.