Assertion: Friction force is a non-conservative force....

Assertion: Friction force is a non-conservative force.
Reason: When a body is moved on a rough surface in a closed path, the work done by friction force is zero.
(A) $\mathrm{A}$
(B) $\mathrm{B}$
(C) $\mathrm{C}$
(D) D

Key Concepts

Friction Force

Friction is a force that opposes the relative motion between two contacting surfaces. Since friction does work that varies with the path taken—often converting mechanical energy into heat—it is classified as a non-conservative force. Its behavior in physical systems is central to understanding energy loss and the limits of motion.

Work Done on a Closed Path

The concept of work done on a closed path relates to the integral of a force over a displacement when an object returns to its starting point. For conservative forces, this integral is zero, reflecting the fact that no net energy is gained or lost. In contrast, for non-conservative forces like friction, the work done over a closed path is not zero, resulting in energy dissipation.

Conservative Force

A conservative force is one for which the work done in moving an object between two points is independent of the path taken. This property implies that the work done by the force around any closed path is zero. Common examples include gravitational force and electrostatic force, where potential energy can be defined based on position with respect to a reference point.

Non-Conservative Force

A non-conservative force is one for which the work done depends on the specific path taken between two points, and the work done around a closed path is not zero. Such forces dissipate energy, typically in the form of heat or sound, making it impossible to fully recover the initial mechanical energy of the system. Friction is a typical example of a non-conservative force.

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