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# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"A new crack at friction," by David A. Kessler. *Nature,* 20 September 2001, pages 260-1.

Although the basic laws of friction have been known for almost 300 years, an explanation of those laws has eluded physicists. This article summarizes work done by Eric Gerde and Michael Marder at the University of Texas, which may lead to a better understanding of friction. Gerde and Marder's model of friction relies on "self-healing cracks," which are described by Kessler using the analogy of moving a large rug. Instead of pulling the rug, one can create a ridge in the rug and then push the ridge the length of the rug, thus moving the rug. The ridge in the rug is like the self-healing crack. An alternative theory says that friction is caused by foreign atoms trapped between two surfaces. Which of the two models explains friction better will have to be decided, but Kessler writes that the "mathematical tour de force" by Gerde and Marder "is a significant step forward in the theory of cracks," which can help in the understanding of phenomena like earthquakes. (An article by Gerde and Marder detailing their research begins on page 285 of the issue.)

*--- Mike Breen*