Two swings are attached to each other below their fulcrums via a steel tube. One of the more interesting results of this coupling is shown here where just one of the two swingers pump, while the other swinger sits still. At first, only the pumper moves, but gradually, the non-pumper starts to move as well. The non-pumper continues to swing ever higher, eventually “stealing” all the kinetic energy from the pumper, thus leaving the pumper at a stand-still—but only momentarily. After a few moments, the energy begins to return to the pumper, eventually leaving the non-pumper at rest. And so it continues, with the energy moving back and forth between the two.