TO GET something moving across a surface, you have to give it an initial
shove. But scientists have never understood why.
Now Martin Muser of the University of Mainz and his colleagues have shown
that dirt is to blame. In Physical Review Letters (vol 86, p 1295) they
suggest that particles of dirt and grime catch in the gaps between the two
jagged surfaces, creating a resistance that has to be overcome in order to get
things moving.
