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Mechanical Properties of Fluids

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Physics Part II

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Class 10 Class 12
What is hydraulic lift? What is its principle? Discuss its working.

Hydraulic lift is a machine which is based on Pascal's law. In these devices fluids are used for transmitting presure. 

Hydraulic lift consists of two cylinders of different cross-sectional areas connected with a pipe. The cylinders are filled with incompressible liquid and frictionless pistons are fitted in both the cylinders as shown in figure below. 

Let 'a' and 'A' be the area of cross-section of smaller piston and bigger piston respectively. The load to be lifted is placed on bigger cross-section and effort is applied on smaller piston.
Let a force 'f' be applied on the smaller piston.

The pressure exerted by f on piston is,

                        P=fa    ... (1) 

Now, according to Pascal's law, the pressure transmitted to bigger piston is also P.

Thus, force on bigger piston is, given by, 
F = PA = Aaf We have, A > a.Let, A = ηaSo, F = ηf 

That is, the transmitted force gets multiplied by a factor η of applied force. 



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.