Frictional force increases on applying brakes. This force always works in the opposite direction of the motion of the vehicle. Due to this reason, vehicles come to rest, after applying brakes.
Vehicles consist of hydraulic brakes. This consist of a cylinder, called a master cylinder. It is filled up with brake oil or hydraulic oil. This is attached to a air resistive piston P, which is connected by a level system L, through a paddle B. Master cylinder is attached to the cylinder (C) through a tube T. Each cylinder consist of two air resistive pistons P1 and P2, which are connected by brake shoes, S1 and S2 respectively.
All the wheels of the vehicle are connected through tube T. When we press the paddle B, of brake by legs, then piston P of master cylinder M move inside the cylinder, through lever system. Due to this, pressure is imposed on the liquid of cylinder. According to Pascal rule, this pressure distributes equally to pistons P1 and P2 So, these pistons press the brake shoes S1 and S2. Here friction force applies a retarding force of the motion wheels. In this way, brake system works.
