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2010 Summer Meeting

2011 AAPT Summer Meeting
July 30-August 3, 2011
Omaha, Nebraska

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PST1F06:

Using Low-friction Carts to Measure Viscosity
  Location: KFC Courts
  Date: Monday, Aug.1
  Time: 8:45 PM -9:30 PM
  Author: Mark Reeves, George Washington University
2029946279, reevesme@gwu.edu
  Co-Author(s): Deepa Raghu
  Abstract: The subject of continuum mechanics is often avoided in the IPLS class, as is a meaningful discussion of nonconservative forces. This is unfortunate since viscosity is essential to understanding the physical aspects of cellular motion and heart disease. I will describe a lab in which students determine viscosity from measurements of the velocity vs. time for metal balls dropped in liquids of various viscosities from air to glycerin, and measure kinematics of the balls falling under the influence of gravity. The balls pull low-friction carts, which allows for a very small driving force and also to measure the position and velocity of the ball continuously. The students observe a variety of behaviors ranging from free fall to reaching terminal velocity. Students measure the position of the cart by an ultrasonic transducer or a photogated pulley, as the weight pulls it down the track. There are a number of non-ideal experimental aspects such as viscous drag on the string and the short drop that doesn't allow attainment of terminal velocity in less viscous liquids. These allow the students to think more deeply about the physics of realistic conditions and make use of Taylor series for their data analysis, should this be desired.
  Footnotes: This research is supported by the NSF/CCLI program. More information can be found at http://www.phys.gwu.edu/iplswiki/index.php/Laboratories
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