The reason for the minus sign will become evident later. This location is called the datum or reference location for gravitational potential energy. This location is called the datum or reference location for elastic potential energy. A force is said to be conservative if the work it does depends on only the starting and ending points of the displacement and not on the path connecting the starting and ending points. Gravitational and electrical forces are conservative.
Friction is non-conservative because the amount of work done by friction depends on the path.
One can associate a potential energy with a conservative force but not with a non-conservative force. Using conservation laws opens up another way of solving mechanics problems that can be very useful. If so, compute the initial value of the conserved quantity and then the final value of the conserved quantity. Step Three Equate the initial and final values and solve for the unknowns in terms of the knowns. As in all physics problems, make sure the units check out and as the final step, make sure your final answer seems reasonable.