The Engineer posted on November 10, 2006 
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Also called Pascal's Principle

Pascal's law — developed by French mathematician Blaise Pascal — states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container. 
Definition of pressure:
If F is the magnitude of the normal force on the piston and A is the surface area of a piston, then the pressure, P, of the fluid at the level to which the device has been submerged as the ratio of the force to area. 

Since the pressure is force per unit area, it has units of N/m^{2} in the SI system.
Another name for the SI unit of pressure is Pascal (Pa) 

An important application of Pascal's law is the hydraulic press. A force F_{1} is applied to a small piston of area A_{1}. The pressure is transmitted through a liquid to a larger piston of area A_{2}. Since the pressure is the same on both sides, we see that P = F_{1}/A_{1} = F_{2}/A_{2}. Therefore, the force F_{2} is larger than F_{1} by multiplying factor A_{2}/A_{1}. Hydraulic brakes, car lifts, hydraulic jacks, and forklifts all make use of this principle. 
