Dump trucks, bucket lifts, power steering, car breaks, barbershop chairs and many industrial machines all use hydraulic systems to operate. Hydraulic systems make use of two pistons that are filled with an incompressible, pressurized liquid. When force is applied to liquid in one smaller piston, the pressure is equalized into the larger piston which, because of its larger area, creates a magnified force.
Hydraulic systems almost always use some sort of oil in connected pressurized pistons. When force is applied to a smaller piston, the pressure of the liquid equalizes throughout all pistons, and since the pressure is equal in pistons of greater area, the larger pistons produce a magnified force. The reason this works is because of Pascal's Principle, which states that when pressure is applied to a incompressible fluid, the pressure is transmitted throughout the entire fluid.
Many machines make use of the amazing power of hydraulics. There are simple applications like office chairs and bike brakes, and large and powerful machines like dump trucks and hydraulic presses. In every case, a small amount of force can be applied that gets multiplied into a large amount of force. When someone presses down on the handle of an office chair, because of the hydraulic system the chair has enough force to lift the person up. Hydraulics have made huge industrial processes much easier and are found in almost every factory and industry world-wide.