Set of three coupled inverted pendulums on wood base.

One oscillating mass on rod sets another mass on rod oscillating in resonance. The apparatus consists of two sets of masses on light springy vertical rods. In a set, masses are all the same, but the rods differ in length. The two sets are weakly coupled by a horizontal bar. When mass 1a oscillates, mass 1b starts to oscillate in resonance (but 2a, 2b, 3a & 3b do not oscillate). When mass 2a oscillates, mass 2b oscillates in resonance, etc. Note: Mounting screw must be slightly loose for the demo to work. Mass on light springy rod. Pull and let go.