1 Pascal's principle

Consider a liquid in a container fitted with a piston. At a point A at depth h below the piston the pressure is P = P₁ + ρgh, where P₁ is the pressure just under the piston. If we add a weight on the piston, the pressure at the piston surface rises by ΔP. The piston does not move because the liquid is incompressible, but the pressure at every point increases by the same ΔP.

Pascal's principle (law): When pressure is applied to a liquid enclosed in a container, the pressure is transmitted in full to every part of the liquid and to the walls of the container.

(If the pressure is increased too much, the container may burst.)