My kids are fascinated when I juggle. I am by no means impressive, and my skill hits the limit at three balls, but it is still enough to get my kids trying it out themselves – much to the chagrin of nearby breakables.
There are many things that could be called "geeky," but juggling ranks in the top ten I think. It’s one of those activities that is a complete expression of human cleverness. Is there anything that can inspire such a mix of silliness and awe? Plus, when done really well, it gives the appearance of defying physics when, in fact, it employs every law of Newtonian physics there is.
Here is a cool project to kill some time on a rainy summer day. This video at Instructables.com shows you how to hack some tennis balls into professional-looking juggling tools.
It works! I can’t keep them out of my kids’ hands. In order to save my windows though, I may make this version for the geeklets.