A spinning copper disc is slowed down when a magnet is brought near it. Note that copper is not a magnetic material. Eddy currents are induced in the disc due to the relative motion of the disc and the magnet. The magnetic fields associated with these currents have such a direction that they oppose the cause that created them in the first place (Lenz rule). As a result they oppose the relative motion between the disc and the magnet and hence the disc is slowed down.
Other videos by Horatiu Pop
Eddy Current Brake from Horatiu Pop on Vimeo.
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