Most trains roll along on metal wheels, but a maglev train does something stranger: it floats. Powerful magnets in the track and in the train push against each other so hard that the whole train lifts a few millimetres into the air and just hovers there, not touching the rails at all. To make it move, the track creates a moving magnetic wave that reaches forward and tugs the train along, a bit like a wave carrying a surfer. Because nothing is touching anything, there is no scraping, grinding or rubbing to slow the train down. The only thing pushing back is the air in front of it. That is why maglev trains can glide along at over 400 kilometres an hour, smoothly and almost silently. In the simulator, turn up the levitation power to lift the train, then add propulsion to send it gliding along the track.
Most people think a maglev floats on a cushion of air, like a hovercraft. In fact it is held up purely by magnetic force, balancing its weight at a small air gap, and the same magnetism, as a travelling wave, also drives it.
What's actually happening
For two centuries trains have meant steel wheels on steel rails, and that pairing has a built-in ceiling. As a conventional train goes faster, the wheels and rails wear, vibrate and eventually start to slip, and the friction at the contact patch wastes energy and generates heat. Engineers wondered: what if the train never touched the track at all? Remove the contact and you remove rolling friction, wheel wear and much of the noise in one stroke. The way to do it is with magnets, and the result is the maglev, short for magnetic levitation.
Two things have to happen for a maglev to work, and both are done with magnetism. The first is lift. Magnets on the train and electromagnets in the guideway are arranged so that they push the train upward, lifting it clear of the track by a small air gap, typically ten to fifteen millimetres. That gap is not as simple as it sounds, because magnetic force grows extremely rapidly as the gap shrinks, roughly as one divided by the gap squared. Left alone the train would either slam onto the track or be flung off, so a fast feedback system constantly measures the gap and tweaks the current to hold it steady. The train effectively balances on a cushion of magnetism, with lift exactly matching its weight at the chosen height.
The second thing is propulsion, and here the cleverness is that the track itself is the motor. In an ordinary electric motor a magnetic field spins around a circle to turn a shaft. In a maglev that motor is unrolled flat along the guideway: coils in the track create a magnetic wave that travels forward, and the magnets on the train lock onto that wave and are pulled along with it, like a surfer carried by a swell. There are no gears, no axles and no contact, just a moving field tugging the train. And because the train touches nothing, there is no rolling friction whatsoever; the only thing resisting its motion is the air it has to push through, which grows with the square of its speed. That is why maglevs shine at very high speed, where wheeled trains struggle: the Shanghai maglev cruises at around 430 kilometres an hour, and test vehicles in Japan have pushed past 600. Float instead of roll, and the old speed ceiling simply lifts away.
A maglev floats on magnetic lift and is pulled by a travelling magnetic wave, so with no contact there is no rolling friction to limit its speed.
- 1Take two ring or button magnets and slide one onto a pencil, then bring the second on with the same poles facing so they repel.
- 2Let the top magnet drop onto the lower one and watch it hover above it, floating on a cushion of magnetic force with a clear air gap between them.
- 3Press the floating magnet down gently and feel the force shoot up as the gap shrinks, exactly the steep behaviour a maglev must control to hold a steady ride height.
Common questions
Magnetic lift changes very steeply with the air gap, so a fast feedback system constantly measures the gap and adjusts the magnet current to keep it stable, holding the train at a steady ride height of around 10 to 15 millimetres.
The track acts as a linear motor. Coils in the guideway create a magnetic wave that travels forward, and magnets on the train lock onto that wave and are pulled along with it, with no rotating parts and no contact.
Because nothing touches, there is no rolling friction and no wheel wear, leaving only aerodynamic drag. Steel wheels overheat and start to slip at very high speed, while a floating train can keep accelerating smoothly past 400 km/h.