So perpetual work/motion machines are impossible, but I've toyed with this idea for a hypothetical, super massive, planetary-scale electrical energy generator for a while. Suppose you had 2 very large moon/planet-sized spherical magnets that were far enough so as to not attract magnetically but close enough to attract gravitationally. You then set these magnetic spheres in motion so that they start orbiting a common center of mass. You then enclose the shared orbit in a hollow, stationary torus. You then coil the torus with wires. My idea is that as the magnetic spheres orbit around their common center of mass, they move along the inside of the hollow torus coiled with cables and generate an electrical current in it forever. And yet it couldn't work forever. I just want to know how or why this system couldn't go on indefinitely.