Question

Which one of the following is not a unit of dynamic viscosity?

(a) Pa-s

(b) N-s/m^2

(c) Poise

(d) Stokes

I have been asked this question in an online interview.

Asked question is from Viscosity in portion Properties of Fluids of Fluid Mechanics

Answer 1

Correct choice is (d) Stokes

The explanation: where F= viscous force, A= area, du ⁄ dx = velocity gradient, μ = co-effcient of viscosity. Therefore,

SI unit of μ is N-s/m^2 = Pa-s and CGS unit of μ is dyne-s/cm^2. 1 Poise= 1 dyne-s/cm^2 and 1 Stokes= 1 cm^2/s. Thus, Stokes is not an unit of μ, rather it is a unit of kinematic viscosity υ.