Pascal's principle

Push on a liquid shut in a container and the extra pressure is passed on, undiminished, to every part of the liquid and to every wall. This is Pascal's principle. Because a liquid hardly squeezes, a small force on a narrow piston makes the same pressure under a wide piston, where it adds up to a much bigger force (force = pressure × area): a hydraulic lift's two pistons obey F1/A1 = F2/A2. A car's hydraulic brakes and the lift in a repair shop work this way, letting a foot stop a car and a small pump raise one.