A while back helped a friend, Dan Busby, in building a Wave Pendulum. I posted a few pictures here, but never got around to posting any videos! Here you can see Dan and some elementary kids geeking out on simple science!
(Here, our wave pendulum is part of the STEAM Carnival by Two Bit Circus!)
Also, here's a self-made video in a back alley of the wave pendulum, un-cut.