LMS Kids: A Hole In The Hand.
Last year, my husband and sons decided to do a few science experiments over the summer. All three of them enjoyed it so much, they've made it an annual event. Here's a graphic of their most recent exercise. I love this one because it's quick, easy, and mess-free! It'd be the perfect experiment to pull out of your sleeve on a road trip or waiting in line—our kids were fascinated (and distracted) for awhile!
Use the tutorial to try it with your kids!