The magnetized coil running along the track, called a guideway, repels the large magnets on the train's undercarriage. This repulsion lifts the train 1 to 10 centimeters ( 0.4 to 4 inches) above the guideway. Once the train is lifted, power is supplied to the coils within the guideway walls. This creates a system of magnetic fields that pull and push the train along the guideway. The alternating current supplied to the coils in the guideway walls is constantly changing the polarity of the magnetized coils. This change in polarity causes the magnetic field in front of the train to pull the vehicle forward, while the magnetic field behind the train adds more forward thrust.