SOME DEMONSTRATIONS FOR NEODYMIUM SUPERMAGNETS. - BILL BEATY obsolete as of: 10/97 THIS PAGE HAS MOVED TO: http://amasci.com/neodemo.html Supermagnets once were fantastically expensive. Tiny cobalt- samarium magnets were priced far higher than any educator could afford. But there currently is another type of magnet that is stronger than C-S magnets and costs far less. This is the Neodymium-Iron-Boron supermagnet. The NIB magnet, or neodymium magnet, is so strong that eye protection must be worn when working with them, because if they slam together, they can shatter and eject chips at dangerous velocities. Many new science demos become pos- sible with NIB magnets because inductive braking effects and repulsion/levitation effects become so strong that they can be directly felt and observed. A 1/2" neodyimum disk magnet costs between $2 and $10. ************************************************************************ WARNING: if you mess with TWO neodymium magnets, you are bound to pinch your fingers if you let them come together. This REALLY HURTS, it's like pliers. Also, you should wear safety glasses, since when two NIB magnets slam together, they tend to launch tiny chips at high velocities. I've had 3/4" magnets fall together accidentally and be completely shattered. The things are brittle! NOT FOR UNSUPERVISED CHILDREN! Always keep magnets away from computers, floppy disks, credit cards, wind-up watches, etc. I've erased several credit cards by accidentally passing an NIB magnet near my pocket, or letting one fall into my lap. ************************************************************************ SUPER COMPASS LOTS MORE DEMONSTRATIONS AT http://amasci.com/neodemo.html Place a Neodymium disk magnet upon a level glass plate (and far from iron objects and other magnets.) The disk will twist around and aim north/south. To guarantee success, you may have to tap upon the glass to lower the static friction momentarily. The alignment force for an NIB magnet is so strong that it acts like a compass even when provided with a very crude bearing! If you suspend an NIB magnet from a thread, it will promptly start swinging in its attempt to aim north. A long stack of NIB disk magnets exhibits even stronger north-south alignment forces. If you close your eyes and move a long stack of NIB magnets in your hand, the Earth's field becomes is just strong enough to feel directly. With practice, you can find the north/south alignment where the tiny torque vanishes. MAGNET RACES Get a piece of 1/4" thick aluminum, 1/16" thick aluminum, and 1/2" thick wood. Each can be 4" to 6" wide and a couple of feet long. Tilt each piece at 45deg or so. Roll or slide an NIB (neodymium, iron,boron) magnet down each plane, or if you can afford to buy them, roll three magnets simultaneously (judiciously separated to prevent interaction!) The Lenz Law electromagnetic braking effect will be pretty obvious. The NIB magnets act as if the 1/4" aluminum is coated with invisible syrup! Try hiding a couple of pieces of thick aluminum behind a thin wood or posterboard plane, and the magnet will suddenly slow down as it slides down the wood and encounters the metal. (Note: thick copper works even better than thick aluminum, but it's harder to find a source.) MAGNETIC BRAKING Roll your Neodymium magnet down an inclined wooden plane. Now roll it down a piece of 1/2" x 1/2" aluminum "U"-shaped extrusion. The magnet will move much slower in the aluminum. And if you affix a couple of thick aluminum plates to different spots on the extrusion (or even below the wood!) you will see obvious braking effects. FEEL THE DRAG DIRECTLY Get a thick slab of aluminum or even copper (thicker than 1/4".) Hold an NIB magnet in your hand and slide it back and forth. You can definintely feel the "syrupy" friction caused by electromagnetic inductive braking effect. If you rub the magnet back and forth for long enough, you will even feel the metal plate's temperature begin to rise. VISIBLE, SLOW FALL Get a length of copper plumbing pipe and drop a small neodymium magnet into it. The magnet will fall slowly. If you choose the magnet and the pipe to give a slip-fit on the magnet, the rate of fall will be very low. If you glue several NIB cylinder magnets end-to-end with repelling faces superglued together (a trick in itself!), the rate of fall will be even slower. And last: purchase some sheets of "magnet viewing film" from Edmund Scientific or other edu. supplier, cut them into strips and tape them around your copper tube, and the audience will be able to "see" the falling magnet as the field pattern moves along the seets of micro- encapsulated film. Or a messier version: wet the copper tube with ferrofluid, and watch the pattern as the magnet slowly falls. HOVERING FALL Get a piece of thick-walled copper pipe about 1-1/4"OD, 3/4"ID, 1/4" wall thickness, and 12" long. REALLY thick walled, more than 1/4" wall thickness is needed. Hold the pipe vertically and drop a 1/2" neodymium disk into it, and it takes a loooong time before it drops out the other end. This demo is well known, but thin-wall water pipe is usually employed. Now do the same again, but LOOK INTO THE TOP END OF THE PIPE. The neodymium disk will be hovering in space as it falls, repelling from the walls as well as being slowed by electromagnetic braking. If you tilt the pipe a bit, the disk magnet will slowly tumble end over end as it floats downwards without touching the sides. Stick two 1/2" NIB disks together for an even slower fall. If you can manage to place a TV camera on the top end and set it for macro close-focus, the whole lecture-hall will be able to see the strange effect. I obtained my copper pipe from ALASKAN COPPER AND BRASS, Seattle WA, 1-800-552-7661. The exact size isn't too important, but the pipe should have a VERY thick wall, 3/16" or 1/4" thick if possible, and the inner diameter should be large enough to allow a 1/2" neodymium disk to have large, obvious clearance all around it as it falls (approx. 3/4" ID. pipe). If they don't stock these exact dimensions, see if they have anything that's close. [ P. Ledlie found another supplier: "Copper and Brass Sales" at 503-254-2600, $65/ft for pipe that's 1" ID. ] INVISIBLE GEAR TEETH Carve a lump of wood or plastic into a 3" cylinder, drill four shallow 3/4" holes in the cylinder surface, and glue four 3/4"-dia. neodymium slugs in the holes. Stick the assembly on a drill bit (even use a hand-powered drill) so you can spin it. When spun near a metal plate, this device acts as an electromagnetic friction drive, or a gear with invisible teeth! Hold a Cu or Al plate near it, and it will push the plate along without touching. Support the spinning cylinder horizontally over a table top with a 1/2" space between table and cylinder, then stick various nonferrous metal plates under it. They will be launched forward. I made a "top" from a 1/4" x 6" aluminum disk with a plastic rod through the center. With practice, one can spin this top up to high speed WITHOUT TOUCHING IT by using the above magnet "gear teeth" cylinder mounted on a power drill. ELECTROMAGNETIC LEVITATION PLATE Attach a large Cu or Al disk to a motor or power drill. Affix this assembly under a plastic or wooden plate for safety, with the spinning metal disk parallel and almost touching the plastic plate. Run it up to speed and hold a neodymium magnet over the plate. You will feel both magnetic drag forces AND repulsion forces. Don't drop the magnet or it will be hurled across the room! Tie your neodyimum magnet to a string, a piece of tape, etc, and affix the other end of the string or tape to the plastic plate so the string stops the drag but not the repulsion. THE MAGNET WILL LEVITATE! Watch out though, if the string lets loose, the EM drag will fling your brittle NIB magnet. Clue: there is a way to levitate a bar magnet above two spinning metal objects which requires no strings. Can you figure it out? See my Maglev page elsewhere on this site, under DOING IT MECHANICALLY. DIAMAGNETIC WATER Place a neodymium magnet in a shallow dish. Fill the dish with water so the magnet is completely covered (about .5cm water above the magnet). Bounce light from a distant small source off the water surface and onto a wall or screen. (sunlight works well.) You will see a uniform oval reflection from the water surface within the circular dish. In the reflected spot of light at the location of the submerged magnet will be a small bright splotch. The bright area is caused by a concave dimple in the water surface. The magnet repels the water slightly, which creates the concavity. Try using less water so there is just 1mm between the magnet face and the surface. This gives a bigger effect, but some people might then suspect that surface tension plays a role. Try looking down into the bowl so you see the reflection of the ceiling. If you move your head back and forth, you will detect a small distortion at the location of the magnet. Add more water so there is 1cm between the surface and the magnet, and the dimple will be *very* shallow and subtle. But it will still be detectable. Repeat the experiment by using a thin plastic dish with the magnet BELOW (no surface tension effects possible!) Idea: use a large number of magnets to write some initials, perhaps cast them into an epoxy block so their faces occupy the same plane. When this is submerged, the magnetic field will spell out the initials in the reflected sunlight. A sort of "chinese magic mirror" image, with the "mirror" being the surface distortion created by magnetism. (Note: put the bowl on a sturdy countertop to stop the water ripples caused by floor vibrations.) DIAMAGNETIC WATER II Haven't tried this one inspired by John Shurner. Levitate a ball of oil submerged in an alcohol/water mixture adjusted for neutral density as follows. Fill a jar with rubbing alcohol, put in a small drip of oil (which promptly sinks.) Next, add small amounts of water to the alcohol and mix slowly (don't break up the oil drop.) Repeat until the oil drop neither sinks nor rises. (This is achieved with only a small percent water in the alcohol.) Use a pipette to add many more oil droplets, so the jar is full of them. Now approach the jar with a NIB magnet. Does it attract the oil? Or, does it repel the water which causes oil to approach the magnet? (John S. may have replicated the Finnish Antigravity experiment: he finds that an HTSC disk chilled in liquid nitrogen causes the oil balls to convect when the jar is held above the superconductor. But does this occur even if electrical shielding and thermal shielding is provided?) WARNING: if you mess with TWO neodymium magnets, you are bound to pinch your fingers if you let them come together. This REALLY HURTS, it's like pliers. Also, you should wear safety glasses, since when two NIB magnets slam together, they tend to launch tiny chips at high velocities. I've had 3/4" magnets fall together accidentally and be completely shattered. The things are brittle! NOT FOR UNSUPERVISED CHILDREN! Always keep magnets away from computers, floppy disks, credit cards, wind-up watches, etc. I've erased several credit cards by accidentally passing an NIB magnet near my pocket, or letting one fall into my lap. Arbor Scientific (www.arborsci.com) has NIB magnets in the form of 1/2" disks. They are priced around $10 each. This may seem expensive, but it is actually lower price than Cobalt-Samarium supermagnets, and they are stronger. And they are worth it just for the amazing things you can do with them. There is also an industrial supplier named Tridus in Paramount, California where you can get them for $3 each, but there is a $50 minimum order. (see below) Arbor Scientific, Ann Arbor, MI, 1-800-367-6695 http://www.arborsci.com Tridus International, 310-408-2222, Paramount, CA (VERY low prices, but $250 minimum. Ask for MgOe:30 neodymium, its plenty strong but not hyper-expensive) www.tridus.com Master Magnetics ??? Magnet Sales Inc., 1-800-421-6692, http://www.magnetsales.com Surplus suppliers: many mailorder suppliers carry 1" trapezoidal NIB magnets removed from computer hard disk head position motors. H&R, Am. Sci. Surplus, All Electronics, and others. See http://amasci.com/supliers.html Or, find old disk drives and tear 'em apart to get those magnets for free!