Is it possible for a system to have negative potential energy?
Yes. All potential energies have an arbitrary "zero point:" the point we designate a zero value for the potential energy. Consider gravitational potential energy. What is the GPE of a ball on the ground? We need to set a coordinate system, so +y upward and the origin at the ground. The GPE of the ball is 0 J. Now let's take our origin to be the top of a tall building. Since upward is positive the y coordinate of the ball is negative. Thus the GPE is also negative.Originally Posted by Candy
We generally need a zero point for any PE, but note that all Physics really cares about is changes in the PE as an object moves from one point to another. So ultimately our choice of origin is whatever we feel like...the choice of origin doesn't affect the problem.