Inc. Old view of friction. The standard frictional force law makes sense only if the two surfaces are identical crystals, fitting together at the atomic level like a pair of gears. New theory and computer simulations show that for mismatched surfaces, a molecular coating of grit explains static friction.
Static friction is everywhere.
It's in that little extra shove at the beginning of a wild downhill sled ride and the first big push that starts a heavy piece of furniture rolling across the floor. But according to the modern microscopic theory of interacting surfaces, it shouldn't exist at all. Now, in the 12 February PRL , a team of physicists has built an analytic theory, backed up with detailed numerical modeling, that may explain why virtually every pair of surfaces lock together and resist sliding. The key is that impurities like dust, dirt, and stray molecules, coat nearly every surface and prevent smooth motion. The laws of static friction were first laid down by Guillaume Amontons, a 17th century French researcher who believed that surfaces have regular jagged edges like the teeth in a bicycle wheel gear.