- Why Magnets Aren't Magic
- 2016 06 15
I've decided that since it takes me roughly two billion years to come out with each new episode, I should be producing other content in the meantime to keep my adoring fans (all five of you) engaged. With that in mind, I'm thinking of doing a series of articles explaining science-y stuff to a general audience. This should accelerate the process of
suffusing myself into every last crenelation of the internet spreading science education to the public. Here's the first installment. Let me know what you think!
Okay, if you put a piece of iron in front of a magnet, the magnet pulls the iron towards it, right? And no matter how many times the two objects are separated, the magnet can just keep pulling on the iron. The magnet keeps doing work on the iron -it keeps pulling it across a certain distance- over and over again, and the strength of its pulling never seems to get any weaker. How can the magnet do that? It must be using up some sort of energy if it's constantly moving another object towards it, right? So does the magnet just have some massive internal power source that keeps it ticking? Is there some sort of magical infinite supply of energy hidden away inside of the magnet, an energy that can be harvested for unlimited use? And if so, why is my electric bill so danged high?
To answer that question, consider this: if you pick up a pen and let go of it, it falls to the ground. You can pick the pen up again, let it go again, and it will fall to the ground again. Ooh, spooky! GRAVITY CAN JUST KEEP PULLING ON STUFF, MAN! IT'S AN INFINITE SOURCE OF ENERGY OMGLMAOBBQ!!! ...Well, no, not really. The problem is that, although you can let go of the pen once and have gravity do work on it, sooner or later the pen hits the floor. At that point, you have to spend energy to pick it back up again (if you don't believe this, try lifting something heavy over and over and see how long it takes for you to get hungry). Because the universe is cruel and unfair, it turns out that the amount of energy you spend in having to pick the pen up off the floor is always going to be greater than the amount of energy you'd get out of the system by letting the pen fall. We call this super-depressing buzz-kill The Second Law of Thermodynamics. It's the reason that magic doesn't exist and all the unicorns are dead, and I hate it.
So going back to our magnets, it's the same idea: sure, a magnet can pull on a piece of iron once until the two are touching, but to make this happen again, you have to spend energy pulling the iron and the magnet apart. In the language of physics, we say that the iron has a "high potential energy" when it's far away from the magnet, and if left to its own devices, it will automatically seek the "low potential energy" of being close to the magnet. Just like the pen, it will try to "fall" from a high potential to a low potential all on its own.
To bring something back from a low potential to a high potential, like dragging the iron away from the magnet or the pen away from the floor, we have to spend energy. The only reason the magnet can "keep pulling stuff towards it" is because you keep dumping energy into the system by pulling them apart again. The bad news is that there's no way to get free energy out of the system in order to cheat the electric company here. The good news is that, to answer the original question, "where does the magnet get the energy needed to keep pulling on stuff," the answer is, the energy comes from you, because the magic was in you all along. D'aww.