Maglev Train

When you were a kid, you may have held two magnets with the same poles close together and felt them push each other away, almost shooting out from your fingertips. A maglev train uses that same invisible force to float a huge body weighing dozens of tons in the air.

There are two main ways to lift a train. One is the attractive type: electromagnets under the train pull up on the rail from below to lift the body, while the gap is constantly adjusted so the train never sticks to the rail. The other is the repulsive type: the train and the rail carry magnets with matching poles, and they push each other apart strongly. An electromagnet, by the way, is a device that acts as a magnet only while electricity flows through it.

The attractive type hovers about 1 centimeter above the rail even when standing still. The repulsive type only builds up its force once it gains speed, so at low speed it rolls on rubber wheels, then rises about 10 centimeters once it passes a certain speed (about 150 kilometers per hour for Japan's superconducting system). Once it is afloat, the body no longer touches the ground, so the rattling and metal-on-metal screech of an ordinary train almost disappear. Best of all, the friction between wheels and rails, which resists a moving object, vanishes completely.

If it can't roll on wheels, how does a floating train move ahead at all? The secret lies in electromagnets packed along the track and the side of the train, which switch their polarity dozens of times every second.

The track magnet just ahead of the train switches to the opposite pole from the train's magnet and pulls the train forward. At the same time, the track magnet just behind the train, which it has only just passed, switches to the same pole as the train and gives it a firm push in the back. The pulling force and the pushing force work together in perfect rhythm.

If you move this pattern of poles quickly forward, like the wave that rolls through a stadium crowd, the train is drawn ahead as if surfing a wave of magnets. It doesn't kick against the ground with wheels. Instead, it treats the whole track as one huge motor stretched out in a line and glides along on a wave of magnetic force.

Losing wheel friction doesn't mean a train can speed up without limit. The train has no friction with the rail, but the faster it goes, the more the air resistance it has to push through grows, and it grows sharply.

Superconducting technology is also used to lift the train high and launch it fast with very strong force. A superconductor is a special material whose electrical resistance drops to zero at extremely low temperatures. With no resistance, a huge current can flow and create a powerful magnetic field, and trains like this have actually set ultra-high-speed records of over 600 kilometers per hour.

Maglev trains have little wear on parts, a low risk of derailment, and are very quiet. But precise electromagnetic coils must be laid along the entire track, so construction is expensive. That is why research follows two paths: low-to-medium-speed lines that quietly connect parts of a city, and long-distance lines that link cities at ultra-high speed.