A simple hydraulic system such as that within a hydraulic jack consists
of two different sized cylinders connected by a pipe.
According to Pascal's Law, pressure exerted
on the smaller piston is transmitted through the fluid to act on internal
surface of the larger piston. Pressure is a property of the system (not
the pistons) and is therefore experienced equally by each piston. Because
each piston has a different surface area, the force exerted on each piston
will be different, even though the pressure is the same.
If the larger piston is twice the area of the smaller piston then the
force on the larger piston will be twice as great. In order to create
that extra force, the smaller piston has to be moved by twice the distance.
Joseph Barmah applied his understanding of this principle when he patented the Bramah Press in 1795.