So suppose we have two objects, both with positive charge Q Coulombs and X meters apart. And now suppose Object 1 has a mass of m1 and Object 2 has a mass of m2. In other words, the charges are identical, but masses are not. So each of these will have an Electric Potential Energy of -QEΔX, because EPE = -QEΔd. Easy peasy, right? EPE = KE, just like PE = KE for a falling object! Just like mgh = (1/2)mv^2, -QEX = (1/2)mv^2. So: EPE = KE, so for Object 1 it's -QEΔX = (1/2)m1v2. and for Object 2 the formula is -QEΔX = (1/2)m2v2. Apparently, that's wrong and I was actually supposed to work it out this way: -QEΔX = (1/2)m1v2 + (1/2)m2v2 It does make sense... but it doesn't. I mean, each object has each of their own potential energy, right? And each object loses that EPE and changes it 100% into KE, right? Isn't that what the potential energy is? I mean, I don't remember doing PE = KE1 + KE2 for a falling object! As far as I know, I've always done: mgh = (1/2)mv2. I don't remember ever making the mass of the earth share the potential energy. If I apply the same concept to gravity, it would be like: mgh = (1/2)mEarthv2 + (1/2)mobjectv2. What!!? I don't remember ever doing that! Help me out here, guys! I am greatly befuddled!