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What is Viscosity?

Viscosity is the fluid property that determines the amount of resistance of the fluid to shear stress.

It is the property of the fluid due to which the fluid offers resistance to flow of one layer of the fluid over another adjacent layer.

In a liquid, viscosity decreases with increase in temperature.

In a gas, viscosity increases with increase in temperature.

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Explain Viscosity in detail?

Viscosity is the property of fluid which defines the interaction between the moving particles of the fluid.

It is the measure of resistance to the flow of fluids.

The viscous force is due to the intermolecular forces acting in the fluid. The flow or rate of deformation of fluids under shear stress is different for different fluids due to the difference in viscosity.

Fluids with high viscosity deform slowly.

Viscosity (represented by μ, Greek letter mu) is a material property, unique to fluids, that measures the fluid's resistance to flow.

Though a property of the fluid, its effect is understood only when the fluid is in motion.

When different elements move with different velocities, each element tries to drag its neighboring elements along with it. Thus, shear stress occurs between fluid elements of different velocities.

(Velocity gradient in laminar shear flow)

The relationship between the shear stress and the velocity field was studied by Isaac Newton and he proposed that the shear stresses are directly proportional to the velocity gradient. 

The constant of proportionality is called the coefficient of dynamic viscosity.

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What is Pressure?

Pressure of a fluid is the force per unit area of the fluid.

In other words, it is the ratio of force on a fluid to the area of the fluid held perpendicular to the direction of the force.

Pressure is denoted by the letter ‘P’. Its unit is N/m2.

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What is Specific volume?

Specific volume is the volume of a fluid (V) occupied per unit mass (m). It is the reciprocal of density.

Specific volume is denoted by the symbol ‘v’. Its unit is m3/kg.

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What is specific weight?

Specific weight is the weight possessed by unit volume of a fluid. It is denoted by ‘w’. Its unit is N/m3.

Specific weight varies from place to place due to the change of acceleration due to gravity (g).

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What is Specific Gravity?

Specific gravity is the ratio of specific weight of the given fluid to the specific weight of standard fluid.

It is denoted by the letter ‘S’. It has no units.

Specific gravity may also be defined as the ratio between densities of the given fluid to the density of standard fluid.

For liquids we take water as a standard fluid with density ρ=1000 kg/m3.

For gases we take air or O2 as a standard fluid with density, ρ=1.293 kg/m3.

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What is Reynolds Number?

Reynolds number is a dimensionless number used in the study of fluid flows.

Reynolds number is the ratio of Inertia force to the viscous or friction force.

It compares the relative strength of inertial and viscous effects.

The value of the Reynolds number is defined as: 

Where ρ (rho) is the density, μ (mu) is the absolute viscosity, V is the characteristic velocity of the flow, and L is the characteristic length for the flow.

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How Reynolds Number for a flow within a pipe is calculated?

Reynolds number for flow within a pipe is calculated from the expression:

Where u is the average fluid velocity within the pipe and d is the inside diameter of the pipe.

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What are dimensionless parameters?

Dimensionless parameters are used to simplify analysis, and describe the physical situation without referring to units.

A dimensionless quantity has no physical unit associated with it.

They arose from dimensional analysis techniques.

These numbers have many applications in fluid mechanics as well as in related subjects like aerodynamics and convective heat transfer.

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What are Newton’s Laws of motion?

Newton described force as the ability to cause a mass to accelerate.

His three laws can be summarized as follows:

First law: If there is no net force on an object, then its velocity is constant. The object is either at rest (if its velocity is equal to zero), or it moves with constant speed in a single direction.

Second law: The rate of change of linear momentum P of an object is equal to the net force F_net.

i.e., dP/dt = F_net

d(mv)/dt = F_net

m X (dv/dt) = F_net

m X a = F_net

Third law: When a first body exerts a force F1 on a second body, the second body simultaneously exerts a force F2 = −F1 on the first body. This means that F1 and F2 are equal in magnitude and opposite in direction.

Newton's Laws of Motion are valid only in an inertial frame of reference.