Disclaimer: not sure if this is actually the most appropriate forum, but it is a question inspired by my work on a homework question...I'm happy for a moderator to move this to a different forum. (But General Physics states: NO HOMEWORK/COURSEWORK QUESTIONS HERE) 1. The problem statement, all variables and given/known data Ok firstly, the question is, why is the potential energy of a system of two opposite charges negative? 2. Relevant equations 3. The attempt at a solution FIRST: my answer is: with charges at infinity PE is zero, and the charges will move towards each other on their own, gaining KE, which must correspond to a decrease in PE, but it was zero, so it must go negative, so any system of two opposite charges with charges not at infinity must have negative PE...is this correct? and SECOND: IS Negative Potential Energy PHYSICALLY MEANINGFUL? Or is it just something we need to conceptualize or cope with in order to accommodate our mathematical models? Is this like the square root of negative one...in that, we just suppose that it can exist and then see what happens when we do? edit: after all, if two opposite charges were at rest stuck to each other, and you pulled them apart, to have some distance r between them, then haven't you increased the potential energy of the system? Why wouldn't it make sense to think of the system of two opposite charges stuck together at rest as having zero potential energy?