Question

Friction can be increased by increasing:
A. smoothness of the surface
B. grease on the surface
C. roughness of the surface
D. lubricating the surface

Answer 1

Hint: Friction is the force which is exerted by one body on another when they slide over one another. Greater the exposure between two surfaces, greater is the molecular interaction between the two bodies and greater is the force of friction between them.

Complete step by step answer:
Friction is a force which comes into play when two bodies slide over each other. When the bodies come in contact, they interact with each other on a microscopic level. If there are any imperfections on the surface of two bodies then then it requires more force to move across those imperfections. This additional force is the frictional force.
Underlying working principle of friction is that when two bodies come in contact with each other and try to slide over each other, their surface may not be smooth and may have bumps and uneven surfaces. This leads to jerky motion which is characterized as friction.
Therefore, if two surfaces are rough then there will be greater friction between them because roughness leads to greater surface to surface exposure between two objects sliding over one another and there is greater intermolecular forces between the surfaces which create the friction.

Hence, the correct answer is option C.

Note:
Friction is an undesirable effect in practical situations which can be reduced by reducing the imperfections on the two surfaces sliding over one another. This can be done by various ways like smoothing the surface, greasing the surfaces or lubricating the surfaces. In case of fluids, it can be reduced by streamlining the surfaces like in the case of airplanes, the streamlining helps in increasing the speed of the plane in air.