Hydraulic Jack

Hydraulic jack is a hydraulic device whose main components are two pistons with a fluid sealed between them (typically a hydraulic oil, which has minimal compressibility). The principle of the hydraulic system is based on Pascal's Law: Pressure induced by external force that acts on the fluid in the sealed container is the same in all points of the liquid.

The force F₁ acting on the first surface S₁ of the piston is creating the pressure ρ in the liquid, which is transferred to all points of the liquid, and thus also the second piston. Equally large pressure ρ pushes on the surface S₂ of the second piston and according to the size of the piston S₂ exerts a force F₂, which may be less than the initial force on the first piston. Everything depends on the size of the piston area. Power is not only transmitted but can also enlarge or reduce.

When lifting a load (car) by a hydraulic device, we can get on a small piston lesser force F₂, but the lift happens along a long path s₂, unlike the large piston, which operate with greater force F₁, but along a shorter path s₁.

Changes of forces and paths correspond to the golden rule of mechanics.