Name: 磁気浮上 (Magnetic Levitation)
Uploaded: 2021-01-14T05:02:50.000Z
Duration: 2 min 9 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

上級受動態

Magnets can be created by running currents through wires, finding a suitable material

that naturally has all the magnetic fields of its atoms aligned, or forcing the magnetic

But there's one more kind of magnetism that all materials exhibit, even those whose constituent

atoms aren't magnetic - though it's so weak that the other kinds of magnetism often overwhelm

it. Basically, an external magnetic field causes the electrons around atoms in a material

to change course, and their new motion generates an opposing magnetic field. This field is

pretty weak, but it does cause the material to be repulsed from the magnet a little bit

- for example, if you hang a wooden toothpick in a magnetic field, the ends will repel the

field and it will end up aligning across the magnetic field. This is a convenient way to

remember the name of this kind of magnetism - diamagnetism - since "dia" means across,

like the "diameter" measured across a circle. Diamagnetic materials will repel a magnet,

and a diamagnetic "compass" will point across the magnetic field - that is, it will orient

As weak as it is, diamagnetism is pretty darn awesome because it's a repulsive effect: any

diamagnetic material will levitate in a strong enough magnetic field! Like this chunk of

graphene, or, since water is diamagnetic, this frog. In principle, humans could also

be levitated this way, though the magnetic fields required would be enormous.

There are also a lot of subtleties we've skated over, like the fact that nitrogen is diamagnetic

even though as an atom it has unpaired electrons - one might think that it *should* be at the

very least paramagnetic. But nitrogen atoms bond to form N2 molecules which have full

outer electron shells and are thus only diamagnetic. On the other hand, molecular O2, as we've

seen, still has unpaired electrons, and it's paramagnetic.

You've probably also seen how superconductors can levitate in a magnetic field, which is

a kind of perfect diamagnetism - not only do the currents in a superconductor create

opposing magnetic fields, they expel magnetic fields from the material entirely. But the

root cause is very very different, and that's a journey for another day.