#### Viscosity and Shear Stress: Interactive Simulation

This simulation was prepared using Mathematica. Download the free Wolfram player, and then download the simulation CDF file (link given below or click on figure to download).

This Demonstration shows the behavior of three immiscible, incompressible fluids in laminar flow. The fluids are layered vertically and subjected to steady-state Couette flow; the top plate moves to the right at a constant velocity, and the bottom plate is stationary. At each height, the velocities represented by the black arrows are relative to the top plate velocity. You can change the viscosities and heights of fluids 2 and 3 with sliders. The velocity distribution shows the impact of fluid viscosity on the fluid’s velocity gradient. The velocity versus height plot indicates the relative slopes (or velocity gradients) in each fluid. All numbers are dimensionless.

**Try to answer these questions before determining the answer with the simulation**. We suggest that you write down the reasons for your answers.

- If the viscosity of a fluid increases, will the slope of the profile increase, decrease or stay the same?
- Think of a way to determine the viscosity of the lower fluid.