The pendulums consist of two 5/16 brass tubes about 16 inches long that are separated by about 5 inches. A brass weight on each rod can be positioned along the length of the rod. They are normally placed about 2/3 of the way from the pivot of the rod. The rods are pivoted on ball bearings. A light coupling spring connects the of the two rods at the far end from the pivot. About a quarter way down the rod, each rod has a horizontal coil spring attached. The end of one of these coil springs is fixed to the supporting structure. The end of the other coil spring is attached to a relay core. The current through the relay is controlled by a variable frequency multivibrator circuit. The period of the two normal modes can be measured in free oscillation and the frequency of the relay can be adjusted to drive either normal mode separately. If the period of the relay drive is set halfway between that of the two normal modes, then both normal modes will be excited with the same frequency. Hmvever, the transient state in which the energy transfers from one pendulum to the other persists for about five minutes before the steady state motion takes over. The experiment is not part of the regular sophomore curriculum but is available to students who wish to investigate the behavior of coupled pendulums.