Magnetic levitation is a method of supporting an object with the repulsive force of magnets and the stability of servomechanisms. The object is thus suspended in the air, counteracting the effects of gravity.
When two like poles, such as negative and negative or positive and positive, of two dipole magnets are placed together, they repel. However, this is not stable because one magnet can easily slide to the side. A servomechanism is used to correct this activity. These servomechanisms include diamagnetic materials, eddy currents or superconductivity.
Pyrolytic graphite is a diamagnetic material, which means it creates a magnetic field in opposition to the externally applied magnetic field, such as that of rare earth permanent magnets. Eddy currents are formed when the Lorentz force on electrons causes them to circulate around the applied magnetic field. A superconductor, when cooled below its characteristic critical temperature, can exclude the magnetic field of a magnet by creating a persistent electric current.
A common form of magnetic levitation in trains utilizes electromagnetic suspension and electrodynamic suspension. Electromagnetic suspension is an attractive force, which uses ferromagnetic rails to guide the electromagnetic vehicle. Electrodynamic suspension is a repulsive force, which uses magnets on the vehicle to lift and support the train.