 As we have seen, Einstein’s equation \(E_o = mc^2\) states that whenever there is a change in the rest energy of an object, there is a corresponding change in its mass (i.e., rest-mass). Although we have not exactly demonstrated it, Einstein’s equation is also interpreted as stating that any object with a non-zero mass (i.e., rest-mass) possesses a rest energy (also sometimes called “internal energy”). 