Question

What are conservative forces? Distinguish the conservative and non-conservative forces among the following:
(i) Gravitational force
(ii) Frictional force
(iii) Air resistance
(iv) Electrostatic forces

Answer 1

Hint:Conservative forces are those forces which are independent of path. Conservative forces depend only on the end points of the path. The most common examples of conservative forces are gravity, electric force and the spring force. Total work done in moving a particle between two points is independent of the path taken.

Complete answer:
A force vector is conservative if the curl of the force vector is equal to zero.Work done in a closed path of a conservative force is always zero.
$W\equiv \,\,\,\int {{{\vec F}}{{.d\vec r = 0}}} $
Conservative forces can also be explained as the forces that conserve mechanical energy.

(i) Gravitational force:Gravitational force is conservative in nature as work done by particles only depends on the initial and the final position of the object.
(ii) Frictional force:It is path dependent force that is why frictional force is non-conservative force. It does not conserve mechanical energy in the moving particle.
(iii) Air resistance:Air resistance is also like frictional force. It is also an example of non-conservative force. Work done by moving particles depends on the whole path of the particle traveled.
(iv) Electrostatic force:It is an example of conservative force as the work done by the body depends only on the initial and the final position of the body. Work done in a closed path is always zero because of its conservative nature.

Note:The most important point to note in this question was that if the work done by the moving body by any applied force depends only on the initial and the final position or we can say the displacement of the body, then the force is conservative in nature. If not, then the force is non-conservative.