Question

Rahul goes to school daily on his cycle. It is his daily observation that he needs to apply more force to start the cycle to move, as compared to when the cycle is in motion. Explain.

Answer 1

Rahul goes to school daily apply the starting cycle motion is zero , cycle is the motion very fast

Answer 2

In the "Adhesion Theory of Friction"
According to this theory, the surfaces in contact, however smooth they may appear, actually have imperfections called Asperities. When one surface rests on the other the actual area of contact is very less than the surface area of the face of contact.

The pressure due to the reaction force between the surfaces is very high as the true contact area is very small.

Hence, these contact points deform a little and cold welds are formed at these points.

So, in order to start the relative sliding between these surfaces, enough force has to be applied to break these welds.

But, once the welds break and the surfaces start sliding over each other, the further formation of these welds is relatively slow and weak and hence a smaller force is enough to keep the block moving with uniform velocity.

This is the reason why coefficient of static friction is greater than coefficient of kinetic friction.