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Question

It is known that a greater force is needed to start a motion of an object on a rough plane than to maintain it moving on the plane.
The reason is that the coefficient of static friction is always larger than the coefficient of kinetic friction.
But why is there such a difference??
Is it because of inertia? Thanks for answering~

WARNING: DO NOT copy from wikipedia as thats nothing for such.

Answer 1

The mechanism of friction is rather complex. In simple terms, when a body is at rest, there exists strong adhesive force between molecules of the object and molecules of the rough plane on their contact surfaces . The object and the plane can be considered in the sense as somewhat [fused] together. Thus a stronger force is needed to break the [fused surfaces] on starting the object in motion.

When the object is moving, [fusion] of the surfaces is not easy. That is, the interaction of the adhesive force between molecules of the object and plane on the point contact is not as strong as when the object is at rest. Thus this gives rise to a smaller kinetic frictional force.