On the edge of friction
(PhysOrg.com) -- The problem exists on both a large and a small scale, and it even bothered the ancient Egyptians. However, although physicists have long had a good understanding of friction in things like stone blocks being pulled by workers into the shape of a pyramid, they have only now been able to explain friction in microscopic dimensions in any degree of detail. Researchers from the University of Stuttgart and the Stuttgart-based Max Planck Institute for Intelligent Systems arranged an elaborate experiment in which they pulled a layer of regularly ordered plastic spheres over an artificial crystal made of light. This enabled them to observe in detail how the layer of spheres slid over the light crystal. Contrary to what one might imagine, the spheres do not all move in unison. In fact, it's only ever some of them that move, while the others stay where they are. This observation...
