In a major technical breakthrough, researchers at the University of Augsburg in Germany have employed a special atomic force microscope to measure the friction between a tungsten tip and a silicon surface. Atomic force microscopy uses a sensitive cantilevered arm with a tip just one atom wide to measure the electrostatic attraction between arm and surface. This allows a 3D map to be drawn up based on the force measurements.
Friction is caused by the dissipation of energy as atoms shift out of place and back again when macroscopic objects slide against each other. As long ago as 1929, the British physicist G A Tomlinson described friction as being due to a "plucking action of one atom on to the other", but it has taken until now to show he was right.
In a variation of the atomic force technique, called frequency modulation lateral force microscopy, the German team drags the tip, which oscillates back and forth, across the surface, giving an excellent measure of friction.
Further reading
F J Giessibl, M Herz and J Mannhart 2002 Friction traced to the single atom Proc. Natl. Acad. Sci. USA 99 12006-12010.