Magnetic damping is a form of
damping
Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples in ...
that occurs when a magnetic field (i.e. a
magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
) travels some distance through or past an
electrical conductor
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gene ...
(or vice versa).
Definition
When a magnetic field moves through a conductor the movement induces an
eddy current
Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnet ...
in the conductor. The flow of electrons in the conductor immediately creates an opposing magnetic field which results in damping of the magnet and produces heat inside the conductor similar to heat buildup inside of a power cord during use. The amount of energy transferred to the conductor in the form of heat is equal to the change in kinetic energy lost by the magnet – the greater the loss of kinetic energy of a magnet (a product of its mass and speed), the greater the heat buildup in the conductor and the more forceful the damping effect. Eddy currents induced in conductors are much stronger as temperatures approach cryogenic levels. This allows for
critical damping for cryogenic applications and testing in the aerospace industry.
Equation
The differential equation of motion of a magnet dropped vertically through or near a conductor, where "M" is the mass of the magnet, "K" is the damping coefficient, "v" is the velocity, "g" is gravity and "a" is the acceleration of the magnet:
:
As gravitational pull increases, the magnet's acceleration as it falls will tend to increase, except to the extent that the damping coefficient the magnet is experiencing (as a result of the conductor) increases, combined with the extent that the ''velocity'' of the magnet ''also'' increases – a magnet moving or falling quickly will have its acceleration (i.e., its increase in speed as it falls) reduced more than one moving or falling more slowly, and this effect on acceleration will be even more pronounced if the damping coefficient of the conductor is high.
Uses
*Compass needle damping
*Vehicle braking
*Roller coaster braking
*Elevator braking
*Speed-dependent torque (which, applied against a coil spring, makes a mechanical
speedometer)
*
Electricity meters
*Stabilization of mechanical gauges such as
weighing scale
A scale or balance is a device used to measure weight or mass. These are also known as mass scales, weight scales, mass balances, and weight balances.
The traditional scale consists of two plates or bowls suspended at equal distances from a ...
s, speedometers, and
galvanometer
A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely.
A galvan ...
s
*Near critical damping at cryogenic temperatures
See also
*
Arago's rotations Arago's rotations is an observable magnetic phenomenon that involves the interactions between a magnetized needle and a moving metal disk. The effect was discovered by François Arago in 1824. At the time of their discovery, Arago's rotations were s ...
observed in 1824
*
Eddy current brake
References
{{Reflist
Electrodynamics
Magnetism