Maglev Trains
If you've been to an airport lately, you've probably noticed that air travel is becoming more and more congested. Despite frequent delays, airplanes still provide the fastest way to travel hundreds or thousands of miles. Passenger air travel revolutionized the transportation industry in the last century, letting people traverse great distances in a matter of hours instead of days or weeks.
The only alternatives to airplanes—feet, ears, buses, boats and conventional trains—are just too slow for today's fast-paced society. However, there is a new form. of transportation that could revolutionize transportation of the 21st century the way airplanes did in the 20th century.
A few countries are using powerful electromagnets to develop high-speed trains, called maglev trains. Maglev is short for magnetic levitation, which means that these trains will float over a guideway using the basic principles of magnets to replace the old steel wheel and track trains. In this article, you will learn how electromagnetic propulsion(电磁推进) works, how three specific types of maglev trains work and where you can ride one of these trains.
Electromagnetic Suspension(EMS)
If you've ever played with magnets, you know that opposite poles attract and like poles repel each other. This is the basic principle behind electromagnetic propulsion. Electromagnets are similar to other magnets in that they attract metal objects, but the magnetic pull is temporary. As you can read about in How Electromagnets Work, you can easily create a small electromagnet yourself by connecting the ends of a copper wire to the positive and negative ends of an AA, C or D-cell battery. This creates a small magnetic field. If you disconnect either end of the wire from the battery, the magnetic field is taken away.
The magnetic field created in this wire-and-battery experiment is the simple idea behind a maglev train rail system. There are three components to this system:
- A large electrical power source
- Metal coils lining a guideway or track
- Large guidance magnets attached to the underside of the train
The big difference between a maglev train and a conventional train is that maglev trains do not have an engine—at least not the kind of engine used to pull typical train cars along steel tracks. The engine for maglev trains is rather unnoticeable. Instead of using fossil fuels, the magnetic field created by the electrified coils in the guideway walls and the track combine to propel the train.
Maglev trains float on a cushion of air, eliminating friction. This lack of friction and the trains' aerodynamic(空气动力学的) designs allow these trains to reach unprecedented ground transportation speeds of more than 310 mph(500 kph), or twice as fast as Amtrak's fastest commuter train. In comparison, a Boeing-777 commercial airplane used for long-range flights can reach a top speed of about 562 mph (905 kph). Developers say that maglev trains will eventually link cities that are up to 1,000 miles (1,609 kin) apart. At 310 mph, you could travel from Paris to Rome in just over two hours.
Electrodynamic Suspension (EDS)
Japanese engineers are developing a competing version of maglev trains that use an electro- dynamic suspension (EDS) system, which is based on the repelling force of magnets. The key difference between Japanese and German maglev trains is that the Japanese trains use super-cooled, superconducting electromagnets. This kind of electromagnet can conduct electricity even after the power supply has been shut off. In the EMS system, which uses standard electromagnets, the coils only conduct electricity when a power supply is present. By chilling the coils at frigid temperatures, Japan's system saves energy. However, the cryogenic(低温学的) system used to cool the coils can be expensive.
Another di

A. Y
B. N
C. NG