Friction on a surface is caused due to the irregularities on that surface. A surface with more irregularities exhibits greater friction compared to a relatively smoother surface. By polishing a surface, these irregularities get evened out and the friction of that surface decreases.

How does polishing and lubrication reduce friction?

The friction is due to the roughness of surface. If we make the surfaces smooth by polishing ,then friction will be reduced. For example a slide in the park is polished to make its surface smooth and reduce friction. Due to reduced friction of a polished ,smooth slide, children can slide down easily.

Can polishing increase friction?

When two surfaces in contact are polished beyond a certain limit and made extremely smooth, they come in intimate contact with each other. Now, the force of adhesion comes into play. Due to this force, the motion of one surface over another surface becomes retarding and hence causes an increase in the friction.