I pry two magnets apart. The magnets attract each other. Say they exert a constant force F on each other. I exert an equivalent force F on each in the opposite direction and pull them apart a distance d (pull each of them d/2 distance). So I have done positive work Fd in total and increased the potential energy of the arrangement by Fd. The magnets have each done negative work -Fd/2 on each other. Me: lost Fd energy Left magnet: lost Fd/2 energy from work done on other magnet Right magnet: lost Fd/2 energy from work done on other magnet The potential energy of the arrangement rose by Fd. Anyone tell me where I messed up? Because conservation of energy doesn't work out.