Figure 2. http://inventors.about.com/library/inventors/blrailroad3.htm
Levitation and Propulsion
Maglev trains use the attractive and repulsive forces of opposite and like charges of a magnet in order to create the levitation necessary to keep the train above the track. Different designs have been created, each having their own pros and cons.
One design uses a T-shaped guidance system where the coils creating the induced magnetic force are located on the track and permanent magnets are located on the car. The repulsive, like charges of magnets are used to make the train hover vertically above the track while opposite charges are used to keep the train from flying off. Both types of charges are used to create an equilibrium so that the train is constantly hovering a certain distance above the track when the magnetic field is active. This equilibrium is possible because the magnetic force increases exponentially as the distance between the track and the train decreases. Maglev trains also use this equilibrium between like and opposite charges of magnets in order to keep the train from deviating off of the track horizontally when turning.
These two feats are accomplished by engineering the trains so that they wrap around a T-shaped guidance system, enveloping the guide way as shown in Figure 2.
Figure 2.
http://inventors.about.com/library/inventors/blrailroad3.htm
The propulsion of the train comes from changing polarity between sections of the track. As the front of the train enters a region of the track, it is pulled forward by the magnetic forces of that section. At the same time, the previous section of the track is changed in polarity to propel the train forward from the back. This concept is portrayed in Figure 3.
Figure 3. http://www.skytran.net/press/sciam02.htm