Question

State and explain Newton's law of viscosity.

Answer 1

Statement:

The viscous force acting on any layer in a streamline flow is exactly proportional to the area (A) and velocity gradient `((dv)/dx).`

Explanation: 

Let A be the area of layer.

`(dv)/dx`be the velocity gradient

F be the viscous force.

∴ By Newton's law of viscosity,

`F ∝ A ((dv)/dx)`

`F = η A (dv)/dx`

where η is constant called coefficient of viscosity of the liquid.

∴ `η = F/(A((dv)/dx))` 

`η = F, if A = 1 m^2 and (dv)/dx = 1 m.s^-1.`