What accounts for the difference between static and kinetic friction?
We have said in lectures that the static friction force increases as the applied force increases up until some limit when motion occurs. It is the threshold of motion which is characterised by the coefficient of static friction. The coefficient of static friction is typically larger than the coefficient of kinetic friction, and we have assumed the kinetic friction is constant over the range of speeds we will study. You do not need to apply quite as much force to keep an object moving as you originally need to break free of the static friction regime. Why is this? To answer this question we can study either the microscopic or macroscopic view. Microscopic view Let us take a box on a table top. Microscopically, the box sits on top of the table and covalent bonds and electrostatic forces form between the box’s surface and the table top. The box cannot move until enough force is applied to break these bonds. As long as the box continues to move, few new covalent bonds can form and there is
