Pascal's Law, also known as Pascal's Principle, states that pressure applied to a confined fluid is transmitted equally in all directions throughout the fluid. This fundamental principle of fluid mechanics was formulated by French mathematician and physicist Blaise Pascal in the 17th century and forms the basis for all hydraulic systems used in modern engineering.

The practical significance of Pascal's Law lies in its ability to multiply force. When a small force is applied to a small-area piston, the resulting pressure is transmitted through an incompressible fluid to a larger-area piston, producing a proportionally larger force. This mechanical advantage is calculated by the ratio of the output piston area to the input piston area.

In a hydraulic system, force amplification occurs because pressure is defined as force per unit area (P = F/A). When you apply a force to a small piston, you create a certain pressure in the fluid. This pressure acts uniformly on all surfaces in contact with the fluid, including a larger output piston.

Since the output piston has a larger area, the same pressure produces a proportionally larger force. For example, if the output piston has 10 times the area of the input piston, the output force will be 10 times greater than the input force. This principle enables humans to lift heavy vehicles with car jacks or operate powerful hydraulic presses with minimal manual effort.