Question

A Static fluid can have ___________

(a) Zero normal stress and non-zero shear stress

(b) Non-zero normal and shear stress

(c) Negative normal stress and zero shear stress

(d) Positive normal stress and zero shear stress

I have been asked this question by my college director while I was bunking the class.

This key question is from Non Newtonian Fluids topic in section Fluid Flow and Mixing of Bioprocess Engineering

Answer 1

The correct answer is (c) Negative normal stress and zero shear stress

For explanation: Fluid with zero shear stress within it is known as static fluid. When ever fluid moves it undergoes continuous deformation due to shear (caused due to viscosity of the fluid). So when the fluid is in rest no shear stress develops and only normal stress exists. So static fluid has zero shear stress.