Confused at a higher level

The view from Carleton College's physics department

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Posted by Arjendu on September 23, 2008

couple of quick links that I’ve already shared with my students in intro mechanics, and that you readers out there might enjoy:

One, on how we don’t really understand friction completely yet, is from Physical Review Focus, and is written by David Ehrenstein of the American Physical Society.
It’s no surprise that a block sliding across a table is slowed by
friction, but for small enough crystals, theory and a few
experiments suggest that frictionless motion may be the norm. Now,
in the 19 September Physical Review Letters, a team of researchers
pushing nanometer-sized metal blocks across an ultra-clean
graphite surface reports that some of them skate freely, while
others resist. The results support a theory that friction arises
only when extra atoms get trapped between the surfaces. This insight
into the origins of friction may be important for researchers
developing nanoscale machines that include sliding parts.

Dirk Dietzel et al., Phys. Rev. Lett. 101, 125505
Link to the paper:
COMPLETE Focus story at

The other is a video of a Mythbusters episode on exactly how difficult it is to separate two intervowen phone-books. It’s kinda amazing. Same principle as a gecko: surface area increases friction tremendously!



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