4F10.10 - Rotational Shear Forces - Glycerin and Ink

Code Number:
Demo Title:
Rotational Shear Forces - Glycerin and Ink
Shear Forces
Area of Study:
Heat & Fluids
Glycerin, Ink, Disposable Syringe, 600 ml Beaker or Larger, Large Test Tube, Rotating Table (Either the Rotating Air Table or a Rotating Platform), and Rheoscopic Fluid.

 Clamp the test tube so that it is inserted into the middle of the beaker.  Make Sure It Is Centered.  Fill with glycerin (chilled glycerin works best).  Inject a vertical column of ink into the glycerin with the syringe.  Rotate the table a certain number of times and watch the ink seem to diffuse in the glycerin.  Now rotate the table the same number of turns in the opposite direction and watch as the ink recombines into the original column.  NOTE: Do not wait to long between the diffusing and recombining operations.

The Rheoscopic fluid is an easy way to show shear planes and fluid dynamics.

Shear forces in glycerin can also be demonstrated quite easily by filling a beaker with some of the reclaimed glycerin we have on hand and then placing a rotating rod in the center that is driven by a variable speed power drill.  Scatter some Lycopodium powder on the surface of the glycerin to enhance the visual effect.  A slow rotation rate is all that is necessary.  The rotating rod must not have any wobble when spinning.

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