In the physical sciences, Pascal's law or Pascal's principle states that "a change in the pressure of an enclosed in compressible fluid is conveyed undiminished to every part of the fluid and to the surfaces of its container." 
1.The underlying principle of the hydraulic press 
2.Used for amplifying the force of the driver's foot in the braking system of most cars and trucks. 
3.Used in artesian wells, water towers, and dams. 
4.Scuba divers must understand this principle. At a depth of 10 meters under water, pressure is twice the atmospheric pressure at sea level, and increases by about 105 k Pa for each increase of 10 m depth.
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Whenever any pressure is applied to any part of boundary of a confined fluid  it is transmitted equally in all directions irrespective of the area