In a maglev system, the train is not only held up by magnets (often using some superconducting electromagnets) but also pulled forward by these magnets. Air friction will gradually slow the train down if the changing electromagnets arenít timed to pull it forward.
If the train needs to be stopped more quickly, the same magnets that pull it forward can be set to push it back. When they do, instead of requiring electrical energy input, they generate electrical energy output, which can be stored in batteries for later use. A similar system is used on some hybrid cars with electrical motors. When braking, the motor converts the mechanical energy of the carís motion back to electrical energy.
Hereís a possible experiment. Take a small battery powered dc electric motor. Disconnect the battery and replace it with a small resistor. Now turn the axle. There should be a measurable voltage across the resistor. The same device that converts electrical energy to mechanical energy can work in reverse to convert mechanical energy to electrical.
We suspect that maglev trains, which ordinarily have wheels as back-up for when the maglev fails, also have conventional brakes on the wheels for emergencies.
Adam and Mike
(republished on 08/02/06)