Question

Friction between two surfaces can be _______ by polishing the surfaces. Fill in the blank.
A. increased
B. decreased
C. the same
D. can’t say

Answer 1

Hint:Any unpolished surface is rough enough for anything to slide over it easily because of the irregularities on the surface. Therefore, the surface is smoothened or polished so that the irregularities deform into a smooth surface.

Complete answer:
Any unpolished surface contains full of irregularities. If one tries to slide any two surfaces that are unpolished, then the friction will be more. One needs to apply a greater amount of force. When two bodies are in contact with each other, the resulting friction is known as dry friction or sliding friction. The force needed to maintain this motion is called the frictional force.
The law is as follows: The force needed to overcome friction and to drag one object on another depends on the normal force between the two surfaces that are in contact. If one polished the two surfaces that are in contact, then the bumps or irregularities between the two surfaces in contact are smoothened. Due to this smoothness, the two surfaces can slide over each other easily and the friction decreases. More the smoothness less is the friction. Therefore, Friction between two surfaces can be decreased by polishing the surfaces.

Hence, option B is the correct answer.

Note: If the two rough surfaces in contact (slider and plane) are made up of the same material, for example copper, are lifted to a vertical position, the slider will not fall off. This is because, when atoms of the same kind are in contact with each other, there is no way for the atoms to know that they are in different pieces of copper.