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Mechanical Properties of Fluids

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Class 10 Class 12
Derive an expression for excess of pressure inside a soap bubble.

Consider a soap bubble of radius R and surface tension T.

There are two free surfaces of soap bubble. Due to surface tension the molecules on the surface film experience the net force in inward direction normal to the surface.

Therefore there is more pressure inside than outside.

Let pi be pressure inside the liquid drop and po the pressure outside the drop.

Therefore excess of pressure inside the liquid drop is,

p =p1–Po

Due to excess of pressure inside the liquid drop, the free surface of the drop will experience the net force in outward direction due to which the drop expands.

Let the free surface be displaced by dR under isothermal conditions.

Therefore excess of pressure does the work in displacing the surface and that work will be stored in the form of potential energy.

The work done by excess of pressure in displacing the surface is,

dW= Force x displacement

= (excess of pressure x Surface area) x displacement of surface

Increase in the potential energy is given by,

dU = surface tension x increase in area of the free surface

From (1) and (2)

p is the excess of pressure inside a soap bubble.

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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.
854 Views

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

No. Intermolecular and inter-atomic forces do not obey the inverse square law.
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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.
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What is fluid?

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

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What is hydrodynamics?

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