A "New" Viscosity Instrument And Exercise

Although mathematical derivations can explain the individual parameters, and many commercial devices are available to accurately measure the behavior, students still seem to have difficulty understanding the physical implications of viscosity; the interaction between shear stress and strain rate. To assist in overcoming this conceptual hurdle, the author designed and built an inexpensive and versatile experimental device and accompanying laboratory exercise for Mechanical Engineering Technology students. It combines the basic aspects of a traditional rotary viscometer with a purely mechanical measurement system that allows students to clearly visualize and experience first-hand the reaction to viscous shear stress on a stationary drum in response to a concentric rotating cup containing the test fluid. This paper describes important design features of the device, constructed from an “antique” Garrard turntable, and the major conceptual topics students must understand in order to complete their laboratory exercise.