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Code Number: 4F10.10
Demo Title: Rotational Shear Forces - Glycerin and Ink
Condition: Good
Principle: Shear Forces
Area of Study: Thermodynamics
Equipment:
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.
Procedure:
Fill the gap between the inner rotating cylinder and the outer container with glycerin. Be careful as any air bubbles that result will have to be allowed to bubble up before the demo can be done. Carefully insert a thin line of the dye/glycerin solution using the syringe with long needle. Turn the handle about 3 times in one direction and observe. Turn the handle in the other direction until the line of dye/glycerin is recombined. You can do this demo several times in a row without replacing the initial glycerin if you thoroughly mix everything after the first attempt. The glycerin will have a blue tint, but it does not affect the concept. Cool glycerin seems to work well for this demo and it can be found in the fridge. You can also reclaim the final blue glycerin for use in other demos where the color does not matter. You can make a case for time reversal with this demonstration as you can start with a thin line of dye and also end with a thin line of dye if you are careful.
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.
References:
- Donald E. Rehfuss, "Current Concepts Consolidated", TPT Vol. 42, #2, Feb. 2004, p. 103.
- Stephen J. Van Hook and Michael F. Schatz, "Simple Demonstrations of Pattern Formation", TPT, Vol. 35, #7, Oct. 1997, p. 391.
- J. T. Lloyd, "Lord Kelvin Demonstrated", TPT, Vol. 18, #1, Jan. 1980, p. 16.
- V. V. Raman, "Where Credit Is Due: The Gas Laws", TPT, Vol. 11, #7, Oct. 1973, p. 419.
- John P. Heller, "An Unmixing Demonstration", AJP, Vol. 28, #4, Apr. 1960, p. 348.
- Richard J. Fitzgerald, "String Formation in Complex Fluids", Physics Today, Vol. 67, #3, Mar. 2014, p. 21.
- Russell J. Donnelly, "Recollections of Chandra", Physics Today, Vol. 64, #6, June 2011, p. 8.
- Ashley G. Smart, "Exploring the Extremes of Turbulence", Physics Today, Vol. 64, #1, Jan. 2011, p. 18.
- Wolfgang Rueckner, "Reversible Fluid Mixing", PIRA Newsletter, Vol. 14, #1, Mar. 1999, p. 4.
- "S-270. Glycerine Cylinder", DICK and RAE Physics Demo Notebook, 1993.
- G. D. Freier and F. J. Anderson, "Hm-2", A Demonstration Handbook for Physics.
- Jearl Walker, "4.131. Unmixing a Dye Solution", The Flying Circus of Physics with Answers.
- Robert Ehrlich, "I.11. Apparent Violation of the Entropy Law", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 124 - 125.