Newton's laws for viscosity
Answers
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Newton's viscosity law's states that, the shear stress between adjacent fluid layers is proportional to the velocity gradients between the two layers. The ratio of shear stress to shear rate is a constant, for a given temperature and pressure, and is defined as the viscosity or coefficient of viscosity.
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Viscosity is a quantitative measure of a fluid’s resistance to flow. It determines fluid strain rate generated by a given applied shear stress. Viscosity is caused by cohesive force between molecules of liquid & by collision between molecules of gas.
Newton’s Law of Viscosity:
Consider a flow in which fluid particles move in a particular direction maintaining straight, parallel lines. For considering Viscosity, Newton proposed some fundamental assumption.
He proposed that,
Firstly "When a flow is adjacent to surface stick to it & have zero velocity relative to the boundary which is called No slip Condition.Other fluid particles attempting to slide over them are retarded because of an interaction between faster & slower moving fluid, a phenomenon that gives rise to shearing force."
Secondly "Shear stress on an interface tangent to the direction of flow is proportional to distance rate of change of Velocity."