Question

Please explain what static friction is.

- If an object slides across a table and stops, is there static friction still acting on it? Or is there no friction at all?

- Please give some examples of static friction and how to identify them in a problem.

Answer 1

Static friction is a self-adjusting force and changes its value according to the external force which is being applied to an object. It ceases to act after it hits its maximum value. After crossing its value a new type of friction called "Kinetic friction" starts acting on the object(Which is less than the static friction).

If an object slides across a table and stops, there is no static friction acting on it. In fact no friction at all.

Lets an object is held on a rough table whose coefficient of static friction is . Now I apply a force(less than the maximum static friction) on the object, the object doesn't move since an equal amount of static friction is applied on the object by the surface of the table. If we increase the value of the external force, the opposing static friction increases its value by the same amount and the object still remains at rest. When I hit the maximum static friction force or greater, the object starts moving and static friction stops acting and kinetic friction starts acting.