Question

Assertion :Static frictional force is self adjusting, for the given two surfaces. Reason: Sliding frictional force between two given solid surfaces is independent of surface area of contact.

• 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

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

Static friction is considered as a self adjusting force because it wants the objects to remain at rest and not move. Therefore if an external force is applied the static friction will be equal the magnitude of external force.

Although a larger area of contact between two surfaces would create a larger source of frictional forces, it also reduces the pressure between the two surfaces for a given force holding them together. Since pressure equals force divided by the area of contact, it works out that the increase in friction generating area is exactly offset by the reduction in pressure; the resulting frictional forces, then, are dependent only on the frictional coefficient of the materials and the force holding them together.

There is no relation between the self-adjusting characteristics and its independency of surface area of contact,