Lesson 1.2c Definition of Viscosity

Goals You can:

  1. Explain the meaning of stress, shear stress, normal stress, rate-of-shear-strain, velocity gradient
  2. Explain the meaning of a Newtonian Fluid and a Non-Newtonian Fluid. Give examples of fluids in each of these categories.
  3. Relate shear stress and velocity gradient using the definition of viscosity (Eq. 1)
\begin{align} \tau =\mu \frac{dV}{dy} \end{align}


  • Shear stress (i.e. viscous stress) causes head loss, pressure drop, drag, energy loss etc. It is of paramount importance in many practical applications.


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