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The coefficient of viscosity is equal to the ratio of shear stress to shear strain. True or False?(a) True(b) FalseI have been asked this question by my school teacher while I was bunking the class.Origin of the question is Fluids Mechanical Properties topic in division Mechanical Properties of Fluids of Physics – Class 11

Answer»

The correct choice is (B) False

The best I can explain: Imagine a fluid element with its bottom LAYER having zero velocity and upper layer, at a height ‘h’, having velocity ‘V’.As the fluid moves, the bottom layer stays as it is, while the other layers will move relative to the bottom layer.So, the strain (=v*Δt/h) continuously increases with time.So we talk about strain rate (=v*Δt/h*Δt = v/h) and not about strain.And we say that stress is proportional to strain rate.Therefore the COEFFICIENT of viscosity is the RATIO of stress & strain rate.



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