Pascal's law basically states that any pressure applied to a fluid inside a closed system will transmit that pressure equally in all directions throughout the fluid. This law is the basic principle that causes hydraulic power in heavy construction machines to work. It is also the principle that causes power brakes on automobiles and other vehicles used in the transportation industry to work. You step on the brake pedal, which pushes a piston connected to the master cylinder of the braking system of the car. To this master cylinder are attached four brake lines, one for each wheel of the car. The pressure exerted on the fluid in the master cylinder is passed equally through the fluid in each of the brake lines to the brake pads of each wheel, which pushes the brake pads against the metal part of the wheel, causing it to experience friction and stop. There are many applications Pascals law would apply to the real world, from how a bulldozer works to how fast a scuba diver can ascend to the surface of the water he dives in.
In the physical sciences, Pascal's law or the Principle of transmission of fluid-pressure states that "pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same." The law was established by French mathematician Blaise Pascal.