Question

A fluid is said to be Newtonian fluid when the shear stress is

• A. directly proportional to the velocity gradient
• B. inversely proportional to the velocity gradient
• C. independent of the velocity gradient
• D. none of these

Answer 1

The correct option is A directly proportional to the velocity gradient

Newtonian fluid: A real fluid which obeys the Newton's law of viscosity is know as Newtonian fluid.
We know that Newton's law of viscosity,
Shear stress:
$\tau \propto \frac{du}{dy}$,
velocity gradient
$\tau =\mu \frac{du}{dy}$

Where $\mu =$ Dynamic viscosity of fluid

Examples of Newtonian fluids:
Water, alcohol, gasoline, air, kerosene