A metallic disc attached to a rod swings between two opposite magnetic poles, and its oscillation dies away very quickly. I thought this happens because the eddy currents formed inside the disc are established in a direction that would cause their magnetic field to oppose the magnetic field which induced them, causing a resistive force on the disc, just like air resistance but much stronger. And since the amplitude is a measure of the total mechanical energy of the disc, and work is done against the "resistive forces", the amplitude decreases. However, my A level book says otherwise. According to my book, eddy currents cause a heating effect which dissipates energy in the disc causing the oscillations to die away. Thoughts on this please?