The familiar heat, wear and general grinding to a halt of friction are all caused by what's going on at the microscopic level when two things rub. And down there, even the smoothest surfaces usually ...

Say we consider a simple experiment of balancing a wooden rod on two fingers. The finger on the left, (1), will remain stationary, whereas the finger on the right, (2), will be moved toward the left.

Consider the block shown above supported by feet at A and B that is at rest on a rough floor. A horizontal force P is applied to the right on the block. As the magnitude of P is increased slowly, two ...