Rare earth magnets are special kinds of magnets, and they behave in a very strange way when exposed to metals โ€” especially copper. The faster they go, the more they slow down. Find out why, and take a look at people trying to force a slow-motion magnet to go fast.

Many people have played around with a magnet, but it's tougher to get your hands on a rare earth magnet. Rare earth magnets are made from rare earth elements. These elements are not rare in and of themselves, but they are so scattered throughout the Earth's crust that it's tough to find large amounts of them in one place. They are prized for their unique qualities. Europium, for example, is the reason why you can see red in your TVs and computer screens. Its job cannot be done by anything else. Rare earth magnets are combinations of these elements, tough to get a hold off, and have both a stronger magnetic field and a lighter weight than most conventional magnets. This combination of lightness and strength allows them to display a strange quality that we don't see in regular magnets.

Moving a magnet around near a coil of wire will induce a current in the wire. Moving current in a wire will create a magnetic field - in other words, an electromagnet. This force opposes the motion of the magnet. This is called Lenz's Law. The faster the magnet goes, the stronger the current it produces. The stronger the current, the stronger the magnetic force. And so, the faster the magnet goes, the more it will be slowed down. Take a look at this, as a falling brick of a rare earth magnet gets slowed down quickly as it picks up speed. (The sudden braking force is also due to the fact that it gets closer to the copper disc.)


The most popular demonstration of this law is with a long, hollow copper tube (see top video). Drop anything else through a copper tube, and nothing much will happen. Drop a rare earth magnet through a copper tube, though, and you will see a long, slightly jerky, slow motion drop. A very weak magnet will stall, mostly, as it picks up speed towards the middle or the end of the tube. A stronger one, like this, will make many little drops as it falls, induces a current, and gets stalled by the electromagnetic force of that induced current. As it stops moving, the current drops away, and it falls again, repeating the cycle over and over.

Top Image of Rare Earth Element Thulium: Alchemist-hp

Via The Naked Scientists and MNN.