The machine in which force is transmitted by liquids under pressure is known as hydraulic machine.
Example: Hydraulic Brakes, Hydraulic Jack
The brakes used for car are hydraulic brakes.
The above diagram describes the working principle of Hydraulic brake.
When the brake pedal is pressed, a piston force breaks fluid from one cylinder along a connecting pipe to another cylinder.
There, the fluid pushes on another piston. This pushes a brake pad against a metal disc attached to the rotating wheel of the car.
The friction slows the wheel.
Liquids are generally incompressible (they cannot be compressed).
When liquid is trapped (closed in a container) and pressure is exerted, this pressure is transmitted to all parts of the liquid.
The force (or pressure) is exerted on small area, but it results on a large area with much force.
Thus the small force applied on a car brake results large force on 4 wheels.
The following system contains fluid
A downward force of 20 N is applied on the piston X.
What will be the upward pressure exerted by the liquid at Y.
A. 4 N/Cm2
B. 1 N/Cm2
C. 20 N/Cm2
D. 40 N/Cm2
Correct answer is "B".
Step 1: Pressure = force /area. Same pressure acts on both the pistons.
Step 2: Force = 20N, Area = 20Cm2
Step 3: Pressure = 20/20 = 1 N/Cm2