A few years ago I was in Manhattan on a short business trip, staying in a hotel in the theater district. I had a free evening, decided to see a musical, and chose a performance of Mary Poppins, hoping to relive some of the fun of the earlier movie version starring Julie Andrews and Dick Van Dyke. I enjoyed the show, but the most memorable and magical moment came at the very end. After Mary Poppins had said her goodbyes to the Banks family, she opened her umbrella and flew away. And this time she didn’t just fly across the...

Theoretical physicists tell us that there are only four basic forces of the universe: gravitation, the electromagnetic force, and the strong and weak nuclear forces. In this book on maglev, we can ignore the two nuclear forces and concentrate on the competition between gravitational and magnetic forces. But what about the force we’re most familiar with, the force of touch—the force the bat exerts on the baseball, the antigravity force our chair exerts on the seat of our pants, the force of air pressure that, as we discussed in the previous chapter, lifts helium balloons and 747s off the...

Most dictionaries define “magnet” as a “body that attracts iron.” As noted in Fact 3 in the previous chapter, although magnets attract iron, they do not attract copper or aluminum, or most other things—plastics, glass, wood, and so on. My granddaughter discovered this shortly after she learned to walk by removing a magnet from our refrigerator door and trying to stick it, usually unsuccessfully, to other surfaces around our house. Magnetic forces are very selective, a property that is not only fascinating but also very useful in separating magnetic materials from nonmagnetic materials. For example, since hay is nonmagnetic...

I have long been a fan of science toys, which are relatively inexpensive but capable of illustrating physical principles in an engaging way. Using them in seminar or lecture can make scientific concepts more accessible and understandable to students from kindergarten to college. The shelves in my MIT office hold numerous science toys, and I have often used the toys related to magnets in a freshman seminar on magnets that I taught there for many years. For example, I often introduced magnetic levitation to the freshmen with the Revolution toy of Figure 4 and then asked them to figure out...

As noted in Chapter 2, it was in 1820 that Hans Christian Oersted first demonstrated that an electric current, that is, electric charges in motion, produced a magnetic field. If the current was carried down a straight wire, the magnetic field produced was directed in a circle around the wire. No magnetic “poles” there. But if many turns of wire are wound together into a coil, the magnetic fields from each turn of wire add together, and the coil becomes an electromagnet with a north pole at one end of the coil and a south pole at the other (Fact...

Winning an Ig Nobel Prize is not nearly as prestigious or as financially advantageous as winning a Nobel Prize, but it often gets as much press coverage. (“Ig Nobel” is pronounced with emphasis on the “bel,” supposedly to avoid the suggestion that there is anything “ignoble” about it.) Initiated at MIT in 1991, the annual October ceremony for granting these satirical awards moved to Harvard a few years later and continues there today. At the Ig Nobels, unlike the formal Nobel ceremonies in Sweden, tuxedos are not required, and you do not get to meet and shake hands with a...

The diamagnetism of frogs is very weak, so levitation of the “flying frog” required an extremely strong magnetic field (and a strong field gradient). The diamagnetism of pyrolitic graphite can be fifty times stronger than that of frogs, allowing levitation of thin flakes of graphite about a millimeter (1/25 in.) above a set of neodymium magnets (Figure 14). But the diamagnetism of an ideal superconductor in low magnetic fields is about 20,000 times stronger than that of pyrolitic graphite! For an ideal superconductor, application of a low external magnetic field produces an opposing magnetic field equal to the applied field...

Up to this point, we have introduced several different types of magnetic forces. They include:

A. Attractive forces between magnets and iron

B. Attractive and repulsive forces between magnets and other magnets

C. Repulsive forces between magnets and conductors with eddy currents induced either by (1) relative motion or (2) pulsed or alternating currents (AC)

D. Repulsive forces between magnets and diamagnetic materials

E. Repulsive forces between magnets and Type I superconductors

F. Repulsive and attractive forces between magnets and Type II superconductors

In this list, “magnets” should be interpreted as including both permanent magnets and electromagnets, with or without...

As noted in the Preface, “Fighting the forces of gravity and friction is one of the things that magnets do best.” The two fights are often very closely related, but we focus now on the fight against friction. Most machines have both moving parts and stationary parts, and friction occurs whenever the surface of a moving part is in contact with the surface of a stationary part. That friction can cause wear and abrasion of one or both surfaces, make motion less smooth, waste energy, and heat parts you really don’t want to heat. One popular approach to fight...

As we saw in the previous chapter, with the help of magnetic antigravity forces rotors spin with greatly reduced friction in watt-hour meters, centrifuges, flywheels, blood pumps, water and wind turbines, and many other rotating machines. In this chapter and the two following ones, we discuss some of the many nonspinning applications in which maglev also plays an important role. So be appropriately warned. With due apologies to Bill O’Reilly and the late Rod Serling, you have now entered another dimension. You are now in the No-Spin Zone.

Harry Potter and the other students at Hogwarts traveled through the air—...

The inventor who inspired the Times reporter to write these optimistic uplifting words nearly a century ago was Emile Bachelet, the first to patent and to demonstrate, via a model car magnetically levitated and propelled along a model track, a “puzzling, if not wonderful” maglev train. In the previous chapters, we have discussed a wide variety of examples of magnetic levitation, including floating globes and flying frogs, rotors and robots, wind tunnels and wind turbines. In this chapter and the next, we turn to the application most commonly associated with the term maglev in the minds of the general public—...

From their earliest days, maglev trains have been associated with the vision of high-speed transport. After seeing Bachelet’s 1912 demonstration of his model maglev train, the Times reporter speculated that it might “presently send whole carloads of passengers whizzing on invisible waves of electro-magnetism through space anywhere from 300 to 1,000 miles an hour.” In the previous chapter, my discussions of German and Japanese progress with maglev trains frequently referred to their achievements of higher and higher speed records. But many people believe that maglev trains also have promise for low-speed transport in an arena that has become known as...

Magnets do lots of important things in modern technology, but in this book we have focused on one—the use of upward magnetic forces to oppose the pervasive downward forces of gravity, the magic of magnetic levitation—maglev. In some cases, like the Levitron and floating desk toys, the aesthetic appeal of levitation was primary. We are so accustomed to the steady pull of gravity that it is undeniably cool to see an object floating in space with no visible means of support. However, in most of the cases we discussed, the main goal of maglev was not aesthetic, but...