Typically, we teach the simplified friction equation of the form Fs = μsN for static friction, where Fs is the maximum static friction, μs is the coefficient of static friction, andN is the normal force pressing the surfaces together. However, this is a bit too simplified, and doesn't work well in cases where the surface area is large and the normal force small. Rather, a better model in such cases would be Fs = μsN + csA, where cs is a new coefficient for the static friction due to contact area.1 Of course, it would help for students to be able to quantitatively measure this, and that's where this paper comes in.

Topics
Friction, Education, Teaching
1.
Edgar Corpuz, Students' Modeling of Friction at the Microscopic Level, doctoral thesis, Kansas State University, 2006 (available for download at http://perg.phys.ksu.edu/dissertations/index.html).
2.
http://dsc.discovery.com/fansites/mythbusters/mythbusters.html.
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© 2010 American Association of Physics Teachers.
2010
American Association of Physics Teachers
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