Eddy current brake
Thus the moving conductor experiences a drag force from the magnet that opposes its motion, proportional to its velocity.
The kinetic energy of the moving object is dissipated as heat generated by the current flowing through the electrical resistance of the conductor.
In some cases, energy in the form of momentum stored within a motor or other machine is used to energize any electromagnets involved.
From Faraday's law of induction, this field induces a counterclockwise flow of electric current (I, red), in the sheet.
As described by Ampere's circuital law, each of these circular currents creates a counter magnetic field (blue arrows), which in accordance with Lenz's law opposes the change in magnetic field, causing a drag force on the sheet which is the braking force exerted by the brake.
When the driver steps on the brake pedal, current is passed through the electromagnet windings, creating a magnetic field.
In regenerative brakes, the motor that drives the wheel is used as a generator to produce electric current, which can be used to charge a battery, enabling the energy to be reused.
Inexpensive air-cooled versions are typically used on chassis dynamometers, where their inherently high-inertia steel rotors are an asset rather than a liability.
Conversely, performance engine dynamometers tend to utilize low-inertia, high RPM, liquid-cooled configurations.
Since they do not actually absorb energy, provisions to transfer their radiated heat out of the test cell area must be provided.
Either a high-volume air-ventilation or water-to-air heat exchanger adds additional cost and complexity.
The eddy current brake does not have any mechanical contact with the rail, thus no wear, and creates neither noise nor odor.
In physics education a simple experiment is sometimes used to illustrate eddy currents and the principle behind magnetic braking.
As one set of authors explained If one views the magnet as an assembly of circulating atomic currents moving through the pipe, [then] Lenz’s law implies that the induced eddies in the pipe wall counter circulate ahead of the moving magnet and co-circulate behind it.
But this implies that the moving magnet is repelled in front and attracted in rear, hence acted upon by a retarding force.
[2]In typical experiments, students measure the slower time of fall of the magnet through a copper tube compared with a cardboard tube, and may use an oscilloscope to observe the pulse of eddy current induced in a loop of wire wound around the pipe when the magnet falls through.
