There exist many methods of determining the viscosity coefficient (η) of a liquid. The most common one in introductory laboratories uses the Stokes viscosimeter. It allows students to obtain a value of η from a measurement of the terminal speed of a sphere falling in a vertically liquid-filled cylinder. This method gives good results when the fluid has a high viscosity (glycerine, oil, etc.). However, for lower-viscosity fluids such as water, the experiment is harder to do using simple instruments, and the results are less precise due to the high terminal speed of the falling spheres. A number of experiments have been described for determining the viscosity of liquids from their rate of flow through a tube.1,2 In this paper we describe a method in which the low-viscosity liquid is allowed to flow through a horizontal capillary tube. The flow speed is low enough to be measured with good precision using a manual stopwatch.

Topics
Education, Flow boundary effects, Capillary flows, Viscosity measurements, Laboratories
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Clifford E. Swartz and Thomas Miner, Teaching Introductory Physics: A Sourcebook (AIP Press, 1997), pp. 301–304.
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A more precise flow model that better describes the actual behavior of the liquid at the entrance of the capillary tube is beyond the level of the introductory level physics course.
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SCHOTT Brasil Ltda., Divisao Vitrofarma, Rua Ivan de Oliveira Lima 155, CEP 20760-600 Rio de Janeiro, Brazil; info.vitrofarma@schott.com.
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Handbook of Chemistry and Physics, edited by Charles D. Hodgman (CRC Press, 1960), p. 2181.
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© 2007 American Association of Physics Teachers.
2007
American Association of Physics Teachers
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