Diamagnetism How to Levitate a Frog




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[♪♩INTRO] Levitation -- it is a time-honored staple among superpowers and magic spells, but it’s not totally fictional. In the real world, we can use magnets to levitate anything from trains to metal desk toys. And you might think levitating something nonmagnetic, say, like a large sack of mostly water, is just for Hermione Granger or Jean Grey -- but it’s not. It can actually happen, thanks to a phenomenon called diamagnetic levitation. And scientists don’t just use it to pretend to be superheroes. It has a lot of potential applications, both in industry and research. We often classify materials as either being magnetic or non-magnetic, but that’s not entirely accurate. See, inside an atom, electrons are constantly buzzing around creating little loops of current. And because of the relationship between electricity and magnetism, that current produces a magnetic field for each electron. Under most circumstances, the direction of all those magnetic fields are random, so they cancel each other out. But when an atom is placed inside another magnetic field, it adds an additional force to the electrons. This essentially changes their motion so that the atom gets a tiny, net magnetic field that opposes the external one. This interaction is called diamagnetism, and because magnetic fields pointing in opposite directions repel each other, it produces a teeny, tiny repulsive force. Every material experiences this -- from a block of wood to an iron bar magnet -- but diamagnetism is only one type of magnetism, and it’s the weakest. There’s also paramagnetism, where atoms become weakly attracted to a magnet in an external magnetic field, and ferromagnetism, which is probably what you think about when someone says “magnetic”. Ferromagnetic materials like iron, nickel, and cobalt can hold onto their own permanent magnetic field long after they’ve been removed from an external one. Even though paramagnetism is still pretty weak, both it and ferromagnetism are much stronger than diamagnetism and will overpower it. But diamagnetic compounds are still pretty awesome. Because they only ever experience a repulsive force when exposed to a magnetic field, it allows them to be levitated. Essentially, they can counter the downward pull of gravity with an upward magnetic push. This was first demonstrated by Werner Braunbeck in 1939, when he used an electromagnet -- a temporary magnet created by running an electric current through a coiled wire -- to levitate small pieces of graphite and bismuth. Then, scientists kind of forgot about it until the 1990s. In the meantime, researchers also experimented with superconductors -- substances that expel magnetic fields at super low temperatures. They can levitate, too, but they use the quirks of quantum mechanics to physically ‘lock’ themselves into place relative to an external magnetic field. It looks really cool, but it’s not quite the same thing as room-temperature diamagnetic levitation. When that research started back up again, scientists were quick to test it out on a lot of seemingly silly items, including hazelnuts, tiny pieces of pizza, and animals, including frogs and a 10-gram mouse. Those animals required a magnetic field 1000 times stronger than a fridge magnet to float -- or about 16 or 17 Tesla -- and they came out of the experience with no negative side effects. Also, watching things float around is a pretty fun day at the lab. If you’re feeling ambitious, you can even demonstrate diamagnetic levitation yourself, using an L-shaped iron rod, some neodymium magnets, and a piece of mechanical pencil lead, which is made of graphite. If you arrange it all correctly, the pencil lead will hover about a millimeter above the magnets. But let’s be honest: The real question here is whether or not you can use diamagnetism to levitate yourself. And the answer is yes. Theoretically. According to magnet designers from the National High Magnetic Field Lab in Florida, you’d need a magnet only slightly weaker than their record-holding 45-Tesla Hybrid Magnet, along with 1 GigaWatt of continuous power consumption to keep the system cool enough to operate. That might seem promising, but all these super powerful magnets have very small experiment spaces -- I’m talking less than 10 centimeters. That’d be pretty snug. So you probably won’t be floating thanks to diamagnetic levitation any time soon, but it does have more uses than just looking cool. For one, it could be used in place of lubrication or ball bearings for truly frictionless transport. Magnetic bearings already exist and are used to support things like maglev trains, but they require sophisticated electronics and a continuous power input. So diamagnetics would be a cheaper option. They could also be used to control satellites in orbit around planets with magnetic fields. Scientists can manipulate the diamagnetic properties of graphite using laser light, and they could develop a system to control a spacecraft’s orientation relative to the planet’s field. And on the research side of things, because diamagnetic levitation operates on an atomic and molecular level, it could be used to simulate weightlessness in Earth-based labs. It’s not a perfect replication, but it could used to model things like how microgravity affects fluid dynamics, crystal growth, or biological tissues -- or, for small enough animals, bone and muscle loss, and cardiovascular changes. And that would be a lot cheaper than launching experiments into space. Scientists are still figuring out how they’ll use all of this, but we know that, whatever diamagnetism ends up being used for, it’s gonna look pretty cool. Thanks for watching this episode of SciShow, which is brought to you by our awesome patrons on Patreon -- like SR Foxly, our president of space! If you’d like to be president of space, or just help support the show, you can go to patreon.com/scishow. [♪♩OUTRO]