Kristin Washburn, age 14, of Dodge City, Kan., for her question:

HOW DOES A LINEAR ELECTRIC MOTOR WORK?

A linear electric motor is a device used mainly to propel high speed vehicles that do not run on wheels. Such vehicles are supported by magnets or by a cushion of air.

A linear electric motor has a row of electromagnets that are turned on and off one after another. The action produces a moving wave of magnetism that travels along the electromagnets just as a wave travels in water. This moving magnetic wave wave propels the vehicle.

There are two types of linear electric motors: the linear induction and the linear synchronous.

A linear induction motor has a row of electromagnets that face a strip of nonmagnetic metal, called a reaction rail. The electromagnets create a moving magnetic field that produces another magnetic field in the reaction rail. One magnetic field pushes against the other and thus moves the vehicle along.

A linear synchronous motor has an electromagnet mounted beneath the track of a vehicle. The vehicle itself also carries strong magnets. The electromagnets create a moving wave of magnetic forces that pushes against the vehicle's magnets and moves the vehicle along just as an ocean wave propels a surfboard.