The Exploratorium has a Tinkering Studio which allows visitors to play and think with their hands, more so than the rest of the museum because people can actually build their own machine.  One of the activities involves creating a Rube Goldberg or Chain Reaction machine, where each action triggers the next action in a whole series of events.

I always get super excited about it when I have a shift in the Tinkering Studio (and usually finagle my schedule so that I do), although sometimes my ideas are a bit grand for the time constraint and materials that I have.  But my slingshot worked!  So this is what I have been doing at work the past few days:

I also really wanted to use a balloon for something other than expelling air, so I made one into a trampoline:

Very productive indeed.