Cue Ball Pendulum
We've always been fascinated by the physics demonstration known as the "Newton's Cradle", where hard steel balls exhibit nearly perfect elastic collisions. We briefly considered building a large Newton's Cradle using cue balls, and that's how we ended up with these two cue balls suspended from the ceiling by long pieces of monofilament string. They were fun to play with for a while, but adding a bowling ball into the mix changed the dynamics of the system in an very interesting way.