Why don’t magnets stick to aluminum? –Les, Los Angeles
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First some facts. Fact number one: magnets only stick to other magnets. Fact number two: big magnets are made up of jillions of tiny magnets. Fact number three: so are the metals the magnets stick to, notably iron, nickel, and cobalt, which are called ferromagnetic materials. The difference is that in the big magnets the tiny magnets are organized–that is, they’re all lined up with their north poles in one direction and their south poles in the opposite direction–while in ferromagnetic materials, the tiny magnets are scattered every which way, and their magnetic fields cancel each other out.
Certain restless intellects out there may now be wondering: what’s with this tiny magnet crap, anyway? That’s where the electron shells come in. As you may have guessed by now, the tiny magnets we’re talking about are individual atoms. Some atoms, such as those in iron, have individual magnetic fields, while others, such as those in aluminum, do not. It all has to do with the electrons.
In his recent treatise on whether singers can break glasses with their voices (May 11), Cecil mentioned “forced oscillation resonance,” in which an external force amplifies the natural vibration of an object, sometimes with destructive results. As an example he cited the 1940 collapse of the Tacoma Narrows bridge. The usual explanation for this disaster is that the wind gusted (“generated a train of vortices,” to be precise) in perfect synch with the bridge’s natural rate of bounce, causing its demise.
