levitation

Levitation is the process by which an object is supported in a gravitational field without being in contact with a solid surface. In practice, levitation occurs when a net upward force balances the weight of the object or when the surrounding medium is manipulated to counteract gravity.

Magnetic levitation relies on magnetic fields to counter gravity. It can be achieved with diamagnetic materials, superconductors, or active electromagnets. Superconductors exhibit the Meissner effect, expelling magnetic fields, and, with flux pinning, can suspend magnets stably. Maglev trains and magnetic bearings are practical implementations.

Diamagnetic levitation uses materials with negative magnetic susceptibility; under strong fields, even small moments can be levitated (examples include bismuth and graphite).

Acoustic levitation uses standing sound waves to trap objects at pressure nodes; useful for contactless handling of small samples.

Optical levitation (optical tweezers) uses focused laser light to trap microscopic particles via gradient forces, enabling biological and physical experiments.

Electrostatic levitation uses electric fields to levitate charged particles; in vacuum or controlled environments, it allows precise positioning.

Historical notes: Human fascination with levitation appears in legends; scientific studies began in the 19th century, with early demonstrations of magnetic and acoustic levitation, and modern milestones include optical tweezers (1980s) and superconducting levitation (late 20th century).

Applications include transportation (maglev), materials processing, precision measurement, and laboratory techniques.