Magnetic levitation is the use of magnetic fields to levitate a (usually) metallic object. Manipulating magnetic fields and controlling their forces can levitate an object.
In this process an object is suspended above another with no other support but magnetic fields.
The electromagnetic force is used to counteract the effects of gravitation. But it has also been proved that it is not possible to levitate using static, macroscopic, `classical' electromagnetic fields.
The forces acting on an object in any combination of gravitational, electrostatic, and magnetostatic fields will make the object's position unstable.
The reason a permanent magnet suspended above another magnet is unstable is because the levitated magnet will easily overturn and the force will become attractive. If the levitated magnet is rotated, the gyroscopic forces can prevent the magnet from overturning.
Several possibilities exist to make levitation viable.
It is possible to levitate superconductors and other diamagnetic materials, which magnetise in the opposite sense to a magnetic field in which they are placed.
A superconductor is perfectly diamagnetic which means it expels a magnetic field (Meissner-Ochsenfeld effect). Other diamagnetic materials are commonplace and can also be levitated in a magnetic field if it is strong enough.Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field.
The induced magnetic moment is very small and in a direction opposite to that of the applied field. When placed between the poles of a strong electromagnet, diamagnetic materials are attracted towards regions where the magnetic field is weak.
Diamagnetism can be used to levitate light pieces of pyrolytic graphite or bismuth above a moderately strong permanent magnet. As water is predominantly diamagnetic, this property has been used to levitate water droplets and even live animals, such as a grasshopper and a frog.
Superconductors are perfect diamagnets and when placed in an external magnetic field expel the field lines from their interiors (better than a diamagnet). The magnet is held at a fixed distance from the superconductor or vice versa. This is the principle in place behind EDS (electrodynamic suspension) maglev trains. The EDS system relies on superconducting magnets.
A maglev is a train, which is suspended in air above the track, and propelled forward using magnetism. Because of the lack of physical contact between the track and vehicle, the only friction is that between the carriages and air. So maglev trains can travel at very high speeds (650 km/h) with reasonable energy consumption and noise levels
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