When two surfaces are polished, the friction coefficient between them decreases. But the friction coefficient increases and becomes very large if the surfaces are made highly smooth. Explain.
When the two surfaces are polished then the deformations, roughness and undulations of the surfaces are reduced and hence, the resistance between them decreases. However, if they are made highly smooth then the resistance between them increases. It is because in highly smooth surfaces, the atoms/molecules of both the surface comes in contact will each other on a large scale and they form a molecular bond between them. This bond is not easy to break, hence, the friction coefficient between them increases.