This is the simplest and clearest explanation I've seen so far. It also helps us understand what a "free energy" device would really entail. It would entail a source of power that was unlimited in comparison to our lives/the lifespan of the earth. Such as solar power. The sun will die, in billions of years, but we don't have to worry about that now.
Oh godamnit. Let me say it again, using the words of the simple sentence you quoted:
Perpetual motion devices using magnets are not perpetual because MAGNETS ARE NOT A SOURCE OF ENERGY
Neither is gravity. Background radiation might be, but there is so little energy in that radiation that it would take an ENORMOUS collector to collect any useful amount of it. In all your examples, it's not a question of "how do we tap it," it's "how much energy is actually in it?" And all your endo/exo-thermic examples are not "free" energy, they are engines that take in energy and covert it into another energy, whether solar to motion, or explosions to heat. This whole think with perpetual motions is actually really quite simple: that energy can not be created or destroyed is a law, and anything that uses energy only converts it into some other form of energy. No other options or "but's." You just can't have something that is moving perpetually. Even in the vacuum of space, not connected to anything, just the fact that you are able to look at it moving around means that light is exerting a force on it and is causing it to slow down. And you can't have something that is generating energy from nothing. It ALWAYS has to come from somewhere.
So our ONLY options are cheap energy generators that convert energy from something else (solar power, chemical reactions, etc), or... nothing. That's pretty much it. If anyone claims they have created a perpetual motion machine or a source of free energy, just ask him where that energy comes from. If he says "magnets," or some other fancy physics gobledegook, he's an idiot.
Except for those stupid electrons that keep on spinning around the nucleus.
Except they don't "spin." They actually exist in a "shell" around the nucleus, with more energetic electrons existing in higher energy levels, higher "shells." They actually move around pretty randomly in that shell.
You only have a chance to find an electron in any given place which means the charge always moves.
The charge oscillates around the nucleus untill energy is injected or extracted.
This oscillation is perpetual motion.