# Pascal's Law and Atmospheric Pressure

## Force acting normally on a surface is called thrust. The force acting normally on unit surface area is called pressure. Thrust is a vector quantity whereas pressure is a scalar quantity. A fluid exerts pressure in all directions. The pressure that a liquid exerts on the sides of the containing vessel, below its free surface is known as lateral pressure, whereas the pressure at the base of the vessel is called pressure. The momentum imparted per second by the molecules to a given surface gives rise to an average force acting on the surface. This average force acting per unit area gives rise to fluid pressure. Laws of liquid pressure are- Pressure at a point inside the liquid increases with the increase in depth of the liquid from its free surface. Pressure at a point inside the liquid at a given depth increases with increase in the density of the liquid. Liquid pressure is same in all directions, about a particular point inside the liquid. Liquid pressure is identical at all points in a horizontal plane at a given depth in an immobile liquid. A liquid seeks its own level. Pascal’s law states that the pressure exerted anywhere in a confined incompressible liquid is transmitted equally in all directions irrespective of the area on which it acts and it always acts at right angles to the surface of containing vessel. Hydraulic press, hydraulic brakes and hydraulic lift are the applications of Pascal’s law. Atmospheric pressure is the pressure exerted by this air. Barometer is a device used to measure the pressure. The change in the some of the factors like altitude, season, temperature, etc. cause a change in the barometric pressure which indicates a change in the air pressure. Aneroid barometer is device which is used to measure the pressure exerted by the atmosphere without the use of the fluids. Gas manometer is an instrument which is used for the measurement of the pressure of the gas.

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