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On the edge of friction
Friction by region: When two microscopic surfaces with the same structure slide over one another, not all particles move at the same time. In fact, the particles in some areas slide (blue spheres), thus distorting their configuration. The other particles (green) stay where they are in the hollows of the surface. © Thomas Bohlein/Ingrid Schofron

On the edge of friction

Precise insight into how two microscopic surfaces slide over one another could help in the manufacture of low-friction surfaces

  • 19 December 2011

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 confirms theoretical predictions and also explains why friction between microscopic surfaces depends on their atomic structure.