If you've ever watched a backhoe at work, you know that it is an extraordinarily powerful tool. First, let's look at the basic idea of a hydraulic system, and then we'll see how a backhoe uses these systems to dig and load such huge amounts of dirt. Hydraulic systems simply transmit forces from point to point through fluid.
Most systems use an incompressible fluid, a fluid that is as dense as it can get.
This sort of fluid transmits nearly all of the original force instead of absorbing some of it. The most commonly used incompressible fluid in hydraulic machinery is oil. In the very simple hydraulic machine shown below, the operator pushes the oil with one piston so that it pushes on another piston, raising it up. Because the second piston has a larger diameter than the first piston, the second piston moves a shorter distance but pushes up with greater force. The basic concept at work is a trade between distance and force.