A. Maglev is short for magnetic levitation, which means maglev trains hover centimeters above a guide rail under the force of powerful electromagnets.

"It's almost like being on an airplane. You're just floating above the track," says Giri Venkataramanan, an electrical engineering professor at UW-Madison.

They may sound futuristic, but Germany, Japan and the United States have experimented with them for years, and a commercial line now runs in Shanghai, China. Their appeal stems from their ability to "fly" safely at more than 300 miles per hour -- speeds that would derail conventional trains.

The electromagnets used in maglev technology have the same attractive and repulsive forces as refrigerator-type, permanent magnets, Venkataramanan said. The difference is that electromagnetic forces are produced by the flow of electric current in a coiled wire.

In one type of maglev train that travels initially on wheels, electromagnets on the train induce currents in electromagnets along the track. As the train accelerates, these induced currents generate a second magnetic field that reacts with the one on the train and repels it, lifting the train up.

Magnetic forces also provide the thrust to move maglev trains. Imagine a series of electromagnets that are excited sequentially to pull the train forward, Venkataramanan said.

"It's sort of like holding a carrot in front of a horse,"he said. "You create an attractive force and then progressively move it, except that the electromagnets producing the force are situated along the train."

-- Produced in cooperation with University Communications

Curious? Look for Curiosities on Thursdays in the Local section. Send questions to: bwilliams@madison.com; 608-252-6130; Curiosities, P.O. Box 8058, Madison, WI 53708."