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Mechanical Properties of Fluids

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Physics Part II

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Class 10 Class 12

The atmospheric pressure at sea level is 760mm of mercury. At what height it will be 740mm of mercury? Take the density of air 1.293kg/m3 constant upto height about 1 km.

Given, atmospheric pressure, P1= 760 mm of Hg
Atmospheric pressure, P2 = 740 mm of Hg
Density of air, ρ = 1.293 kg/m3

Let the height at which the atmospheric pressure is decreased be 'h'. 

Now, Pressure due to h height of air = Pressure due to 2 cm or 0.02 m of mercury. 


1.293 x g x h = 13600 x g x 0.02 

              h = 210 m, is the height at which the atmospheric pressure will decrease. 

Do intermolecular or inter-atomic forces follow inverse square law?

No. Intermolecular and inter-atomic forces do not obey the inverse square law. 

What is fluid?

Any material that can flow is a fluid. Liquids and gases are examples of fluid.


What is hydrostatics?

Hydrostatics is the branch of fluid mechanics that studies incompressible fluids at rest. The study of fluids at rest or objects placed at rest in fluids is hydrostatics.

What is hydrodynamics?

Hydrodynamics is the branch of science that studies about the force exerted by the fluids or acting on the fluids. 

Why solids have definite shape while liquids do not have definite shape?

Solids: Intermolecular forces are very strong and thermal agitations are not sufficiently strong to separate the molecules from their mean position. Solids are rigid and hence they have definite shapes.
Liquids: In liquids intermolecular forces are not sufficiently strong to hold the molecules at definite sites, as a result they move freely within the bulk of liquid, therefore, do not possess definite shapes. Liquids take the same shape as that of the container.