Question

ASSERTION: On polishing the surface, the friction decreases up to certain limit but increases beyond that
REASON: On polishing the surface, the irregularities are cut off but beyond a certain limit the surface molecules exert strong attractive forces on each other.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Answer 1

Hint: Friction can be reduced by reducing the irregularities on a surface. Polishing helps in reducing the friction. On excessively polishing the surface, the bonds of the atoms on the surface start breaking which leads to increase in the irregularities on that surface.

Complete step by step answer:
Friction is the opposing force experienced when two bodies slide over one another.
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. But if we polish that surface beyond a certain limit then friction of the surface increases.
Therefore, we can say that ASSERTION is correct.
Now the reason for increase in the friction on excessive polishing is that on polishing the surface beyond a certain limit, the atoms on the surface of the material start getting removed and the surface molecules exert strong attractive forces on each other which creates new irregularities on that surface and the friction starts increasing.
Therefore, we can say that REASON is also correct and the right explanation of the given ASSERTION.

Hence, the correct answer is option A.

Note:
There exist different ways by which we can decrease the amount of friction in a system. Some of them are given below:
1. Smoothing the surfaces: By polishing a surface, we can remove excessive dents or ridges which increase the amount of friction.
2. Lubrication: Lubricants have oily texture which helps in reducing friction. They fill up gaps and ridges thereby making sliding smoother.
3. Streamlining: Friction can be reduced by making the objects shape streamline which need to move in fluids like liquid and air. E.g. Airplanes have streamlined bodies to reduce friction due to the atmosphere.
4. Rolling motion: Friction is far less in the case of bodies rolling over each other than bodies sliding over each other.