Question

Assertion: The coefficient of friction can be greater than unity.
Reason: The force of friction is dependent on normal reaction and the ratio of force of friction and normal reaction cannot exceed unity.
(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) Assertion is incorrect but Reason is correct

Answer 1

Hint
The coefficient of friction is a measure of dependency between the frictional force and the normal reaction. Its value mostly depends on the material of the body.
$\mu = \dfrac{F}{N}$, where $\mu $ is the coefficient of friction for a body experiencing normal reaction $N$ and frictional force $F$. It is a unit-less, dimensionless quantity.

Complete step by step answer
Friction is the resistance offered by an object to its motion, or another body’s motion over it. It depends on the coefficient of friction which is a material property. The coefficient of friction tells us about how much smaller or greater than the normal force is the frictional force. For most objects, the coefficient of friction lies between 0 and 1. But that does not mean that it cannot be greater than 1. Silicon rubber is one such material that has a coefficient of friction greater than unity. Hence, the Assertion is correct.
The force of friction is calculated as the product of normal reaction and the coefficient of reaction. So, the former part of the Reason is correct. We just saw that the coefficient of friction can be greater than 1, and it is given as:
$\mu = \dfrac{F}{N}$
As this value can be greater than 1, the ratio of frictional force and normal reaction can also exceed unity. Hence, the Reason is wrong.
Thus, the correct answer is option (C): Assertion is correct but the Reason is incorrect.

Note
The lowest coefficient of friction is possessed by a material called PTTE (Polytetrafluoroethylene). It is chemically manufactured and is used as a coating for non-stick pans and other cookwares.