Correct Answer - Option 1 : viscosity
CONCEPT:
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Viscosity: The state of being sticky, thick, and semi-fluid inconsistency, due to internal friction of fluids is called viscosity.
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Newton's Formula of the coefficient of viscosity:
- According to this formula, force is proportional to contact area A and velocity gradient \({Δ v \over Δ z}\)
\(F \propto A{Δ v \over Δ z}\)
\(F =\pm η A{Δ v \over Δ z}\)
where η is the coefficient of viscosity, A is the contact area and \({Δ v \over Δ z}\)is velocity gradient.
EXPLANATION:
According to the principle of continuity, \(A_1V_1=A_2V_2\), if the area is constant speed should be constant.
- But velocity goes on decreasing. This is due to viscosity.
- Due to viscosity, there exists a viscous drag force (like a friction force for solids) which acts in the opposite direction of the flow.
- So the reason for the decreasing speed is viscosity.
- Hence the correct answer is option 1.
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Principle of Continuity: It shows the conservation of mass in a given space occupied by a fluid.
- It says that the mass discharge for steady flow in a pipe is always constant; that is,
ρVA = constant
where A is the cross-sectional area of the pipe and V is the mean velocity.
\(\rho_1V_1A_1=\rho_2V_2A_2\)
If the fluid is incompressible i.e. density is not changing when passing from one place to another place.
\(\rho V_1A_1=\rho V_2A_2\)
\(A_1V_1=A_2V_2\)
