Coupled Pendulums: kinetic energy transfers between the pendulums in a complicated but cyclic way due only to the connecting string. If the two on the left are set to swing, soon the middle sphere is at rest while the two outside swing, then the one on the far left comes to rest and it starts the pattern over on the right. The pattern repeats until the initial energy is dissipated by friction. This desk toy was manufactured in the 1970s with the somewhat unfortunate product name “Mystery Swinger