Figure shows a horizontal cylinder with a piston and three vertical tubes. Liquid has the same level in all the three tubes. This shows that pressure is the same at their bases. Now we push the piston and wait. We find that the level is raised but by the same height in the all the tubes. Thus the change in pressure has been transmitted to all the points without any decrease. (This is Pascal’s law of transmission of pressure).
This is the principle of hydraulic machines.
Example : Hydraulic lift
Figure shows two pistons of areas A1 and A2. They are connected by a liquid. If we apply a force F1 a change in pressure F1/A1 is produced. This, according to Pascal, is transmitted to all the points of the liquid, and hence also at the base of right piston (of area A2). Corresponding to the change in pressure, there is produced a force F2, acting over area A2 ,such that
As A2 >A1, the force F2 is larger than the applied force F1.
Mechanical advantage of a machine is defined as the ratio of load (F2) to effort (F1). There (A2 /A1) is equal to (F2 /F1), the mechanical advantage of hydraulic lift. the large force F2 maybe used to press a drum of rotating wheel, acting as brake. This is the principle of a hydraulic brake.The force F2 maybe used to press big bundles into small for typing ‘Brahma press’ is such a device.