Museum of Science and Industry

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When a current flows through a coil of wire, the coil becomes an electromagnet. The direction of the current determines the polarity of the magnetic field. One side of the coil becomes the north pole, and the opposite side becomes the south pole. As with all magnets, opposite magnetic poles attract and like magnetic poles repel. The magnet pile placed under the coil attracts its opposite pole on the coil and repels its like pole, causing the coil to spin.

Since the arms of the coil only have insulation on one half, electric current only passes through when the uninsulated part of the wire touches the paperclips. When the coil swings around and the insulated part of the wire touches the paperclips, the current is interrupted, stopping the magnetic field for half a turn. When the current flows through the coil again, the two magnetic poles either repel or attract each other once more. After the coil starts spinning, momentum carries it through the part of its cycle when there is no current.

Almost every mechanical movement that you see around you is caused by an AC (alternating current) or DC (direct current) electric motor.

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