Law of Pascal is also known that “Pascal’s Law”, “Pascal’s Principle”, “Principle of Transmission of Fluid-Pressure”.
Consider an incompressible liquid at rest. The law of Pascal applies:
p = pa + 𝜌 ⋅ g ⋅ H
Pascal’s Law
where
• p: the static pressure at the considered point [Pa = N/m2]
• pa: atmospheric pressure (ca. 1 [bar])
• 𝜌: specific mass of the liquid [kg/m3]
• g: gravitational acceleration (9.81 [m2/s])
• H: height beneath the liquid surface [m]).
One can distinguish the following pressure measurement apparatus:
• A manometer usually measures the effective pressure; this is an overpressure (mostly with respect to the atmospheric pressure).
• A vacuum meter measures an underpressure (with respect to the atmospheric pressure).
• A barometer measures the absolute pressure of the atmosphere.
Consider the image given below. The column is filled with water and the ends of each column A and B have been blocked by a piston. If piston A is pressed, what do you think will happen to piston B? Piston B is going to rise up. We have just applied Law of Pascal to our fluid pressure.
Simple Figure
“The external static pressure applied on a confined liquid is distributed or transmitted evenly throughout the liquid in all directions.”
The static pressure acts at right angles to any surface in contact with the fluid. Pascal also found that the pressure at a point for a static fluid would be the same across all planes passing through that point in that fluid. Pascal’s law is also known as Pascal’s principle or principle of transmission of fluid-pressure. In 1653, Pascal law was stated by French mathematician Blaise Pascal.
Pascal’s law can be used in a wide variety of situations. It is the operating principle of different hydraulic machines and hydraulic components, and is also useful in the design of liquid containers, dams, ships, submarines, and scuba diving equipment, just to mention a few.
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