Sympathetic Swing
Two persons should sit in the two swings. First person should oscillate while second should be at rest and while swinging the legs of both the persons should be on the foot rest provided. The energy of the first swing is transferred to the second swing and it starts moving and the first swing now comes to rest. The two swings are acting like two simple pendulums and energy transfer takes place because of the resonance between the swings. This energy transfer may lead to perpetual motion but the energy loss due to friction does not permit this.