Maharashtra BoardEnglish MediumSTD 12 SciencePhysicsMechanical Properties of Fluids3 Marks
Question
State and explain Newton's law of viscosity.
✓
Answer
Newton's law of viscosity: In a steady flow of a fluid past a solid surface, a velocity profile is set up such that the viscous drag per unit area on a layer is directly proportional to the velocity gradient.When a fluid flows past a solid surface in a streamline flow or when a solid body moves through a fluid, the force of fluid friction opposing the motion is called the viscous drag. The magnitude of the viscous drag of a fluid is given by Newton's law of viscosity. If $\frac{d v}{d y}$ is the velocity gradient, the viscous drag per unit area on a layer, $ \begin{aligned} & \frac{F}{A} \propto \frac{d v}{d y} \\ & \therefore \frac{F}{A}=\eta \frac{d v}{d y} \end{aligned} $ where the constant of proportionality, $y$, is called the coefficient of viscosity of the fluid.
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