Why there will be a change in the sole of the shoes after using many days?

See the explanation below

Explanation:

Due to the frictional force, this force acts in the opposite direction to the movement of the person's shoe. This force tends to wear the sole of any shoe. We must remember that the frictional force is defined as the product of the normal force by the coefficient of friction between surfaces.

For this case, it should be the coefficient of dynamic friction between the pavement and the material of the sole of the shoe