Hydraulic machines work based on the principle of Pascal's Law, which states that the pressure exerted on a confined fluid is transmitted equally in all directions. This means that the pressure applied to one part of a confined fluid is transmitted throughout the entire fluid, regardless of the shape or size of the container. This principle is used in hydraulic machines to transfer force from one point to another by using a fluid, usually oil or water, in a closed system of pipes or cylinders.
The force applied to the small piston of a hydraulic machine is transmitted through the fluid, and it is amplified on the larger piston due to the difference in area between the two pistons. This allows a small force to be amplified into a much larger force, making the machine able to lift or move heavy loads with minimal effort.
This is the basic principle that makes hydraulic systems, such as car brakes, lift, cranes, excavators, and many other machines work.