Why learn about potential energy?

At this point, the Work-Energy Theorem gives us everything we need to keep track of the energy of a mechanical system. We can determine which forces do work on the system and calculate how much energy they add to or take away from the system. However, there is a special group of forces that convert the energy of a system from one form to another when they do work. These forces are known as conservative forces. When you do work against a conservative force, that work has been converted into a new type of energy—potential energy. So there is a potential energy that keeps track of the work done by a conservative force. Two of the forces we have talked about so far are conservative forces—the gravitational force and the spring force. The work done by these two forces will allow us to calculate the change in the gravitational potential energy and the elastic potential energy.