# Definition Of Hydraulic Machine

## Definition Of Hydraulic Machine

The machine in which force is transmitted by liquids under pressure is known as hydraulic machine.
Example: Hydraulic Brakes, Hydraulic Jack

#### Hydraulic Brakes

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.

#### Worked Example

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