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Mechanical Properties of Fluids

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Physics Part II

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Class 10 Class 12

A manometer reads the pressure of a gas in an enclosure as shown in the figure. The liquid used in the manometers is mercury and the atmospheric pressure is 76 cm of mercury. 
Give the absolute and gauge pressure of the gas in the enclosure. 

Atmospheric pressure of mercury = 76 mm

The difference in the Hg column in two arms of manometer as given in the figure is 20 cm.

Therefore the gauge pressure is +20 cm of Hg.

Positive sign indicates that the pressure of gas is greater than atmospheric pressure.

Absolute pressure = Atmospheric pressure + gauge pressure 
                           = 76cm + 20cm

                           = 96cm of Hg. 

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. 

What is hydrodynamics?

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

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.

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

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