# Negative electrostatic potential energy

I have an example in my book showing 3 point charges each at the vertices of an equilateral triangle. q1 = +2 microC, q2 = -2 microC, and q3 = +1 microCoulombs. the distance between each is 0.30m. The example calculates the electrostatic potential energy of the charge configuration, obtaining -0.12 J. The example says that because the electrostatic potential is negative, if the charges were released from rest, they would fall together, not fly apart. "They would fall together, because this would lower their potential energy still further (a larger negative value)." I'm having trouble understanding this principle of negative potential energies. Can someone explain this to me? What does it mean exactly to have negative potential energy? I know there can be a negative change in potential energy, and that is easy to understand using the similar gravitational potential energy. And why must the charges fall together, and why must the potential energy be lowered by having a larger negative value?