Suppose a copper (or other conducting) ring is resting on one pole of an electromagnet. When the current is turned on (shown by the red circuit coloring), the ring will fly off the magnet. This is a consequence of Faraday's law of electromagnetic induction. A time-varying magnetic field will induce a circulating current in the ring. The magnetic field thereby produced will cause the ring to be repelled by the electromagnet. This will not happen if a radial slit is cut through the ring, thus preventing any current circulation. For purposes of visualization, the action is shown in slow motion and the disk is stopped in midair before it falls back to the ground.