Conservative force: A force is conservative (i) if the work done by the force in displacing a particle from one point to another is independent of the path followed by the particle and (ii) if the work done by the force in moving a particle around any closed path is zero.
Examples : Gravitational force, electrostatic force and elastic force of a spring are all conservative forces.
Non-conservative force: If the amount of work done in moving an object against a force from one point to another depends on the path along which the body moves, then such a force is called a non-conservative force.
Examples : Forces of friction and viscosity are non-conservative forces.