The eighth marvel of the learned alchemists of Macedonia

Posted on February 13, 2008 by Steve

Primero llevaron el imán. Un gitano corpulento, de barba montaraz y manos de gorrión, que se presentó con el nombre de Melquíades, hizo una truculenta demostración pública de lo que él mismo llamaba la octava maravilla de los sabios alquimistas de Macedonia. Fue de casa en casa arrastrando dos lingotes metálicos, y todo el mundo se espantó al ver que los calderos, las pailas, las tenazas y los anafes se caían de su sitio, y las maderas crujían por la desesperación de los clavos y los tornillos tratando de desenclavarse, y aun los objetos perdidos desde hacía mucho tiempo aparecían por donde más se les había buscado, y se arrastraban en desbandada turbulenta detrás de los fierros mágicos de Melquíades. «Las cosas tienen vida propia —pregonaba el gitano con áspero acento—, todo es cuestión de despertarles el ánima.»
Cien años de soledad

I've taken hard drives apart before, but I never realized that I was throwing the best parts away to get to the shiny platters. Now I know that hard drives contain powerful rare earth magnets, strong enough to hold a wrench to your refrigerator. I harvested a pair from an old drive and rediscovered the childhood pleasure feeling their invisible force and learned a few new tricks.

Neodymium magnets have strength on the order of MRI machines, but without the attending inconveniences because of their small size. Magnetic field strength falls off with the cube of distance from the center of the magnet, so a magnet a few centimeters across doesn't have a far-reaching field compared to a big speaker magnet, and you might be underwhelmed at first. But move a little closer, and the magic begins.

I haven't let my two magnets come in direct contact, for fear of never getting them apart. Putting one in a camera case and the other in my pocket allowed me to securely attach the camera case to my hip without a belt. I managed to fumble one into the toilet and grumpily started rolling up a sleeve, thinking well, there's nothing else for it... But before it was too late I realized that there was another way, and easily dragged the wet magnet up out of its misery with its cousin on the other side of the porcelain, and even applied a few sanitizing flushes before retrieving it. On the other hand, a wooden restaurant table proved too thick to allow the moving-fork prank.

These magnets are strong enough to affect food. I prepared a barbell with grapes on each end of a straw and hung it from the ceiling by a thread. Feeling like Cavendish weighing the Earth, I managed to push the grapes magnetically and tried to create a health scare. No one seemed to mind eating grapes that contain dimagnetic dihydrogen monoxide, though.

The coolest sensation was feeling magnetic braking for the first time. I didn't know what eddy currents are (or courants de Foucault, after their discoverer Léon, the pendulum guy), but now I've felt them. If you run a strong magnet alongside a piece of aluminum or copper, there is an eerie resistance against the direction of motion. Stop moving and the force stops.

There's one more trick I've yet to try—sensing the biggest magnet in the world with my bare hands. According to Wikipedia: "A somewhat larger magnet interacts strongly enough with the magnetic field of the Earth to allow its tendency to align with that field to be perceived directly when holding it."

source for background