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Pressure: Liquid Pressure, Pascal's Law and Upthrust

Liquid Pressure

Liquid pressure is the increase in pressure at increasing depths in a liquid. This pressure increases because the liquid at lower depths also has to support water all above it. We calculate liquid pressure using the equation Liquid Pressure=mass*acceleration due to gravity*depth in liquid. To further prove this formulae,             Here is a link for the video: https://www.brightstorm.com/science/physics/solids-liquids-and-gases/liquid-pressure/?jwsource=cl

we know, pressure is the force applied on unit area

Hence, P= F/A

or, P=  m*g/A           [since, F= mg]
or, P= d*v*g/A          [since, d= m/v or, m= d*v]

or, P= d*A*h*g/A      [since, V= A*h]

Therefore, P=d*h*g   P= liquid pressure

Also, P  h.

And, pressure is measured in Nm-2 in S.I. system. But liquid pressure is also measured in mm of Hg.


Pascal's Law

Pascal's Law, in fluid mechanics, statement that, in a fluid at rest in a closed container, a pressure change in one part is transmitted without loss to every portion of the fluid and to the walls of the container . The principal was introduced by Blaise Pascal (June 19, 1623 - Aug 19, 1662).

Applications of Pascal's Law

Now since you may have understood something about pascal's law here are some of it's application and you will know them through some given videos.


It will be explained through points.

  • Upthrust is a force which pushes upwards on an object submerged in a fluid.

  • Also known as buoyancy force, upthrust is due to the difference is hydrostatic pressure at the top and bottom of the immersed object

  • The force of upthrust is significantly larger than in gases, this is because liquids are much denser than gas

  • Recall that hydrostatic pressure depends on the height (h) or depth that an object is submerged in from P=d*g*h

  • Therefore, the water pressure at the bottom of an object is greater than that at the top of as shown in diagram at the right

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