Tap the balloon a few times and the rubber granules fall off. So what's going on here? Static electricity. Free electrons easily build up on the surface of a balloon. Many of you have probably observed this when rubbing a balloon on your hair and sticking it to wall. The same concept is taking place here. The rubber granules, being small and having a low mass, are easily pulled to the balloon's surface through an electrostatic force. The electrostatic force is greater than the gravitational force trying to pull the granules back to the ground. Thus the granules stick to the balloon.
A bit later I was examining the balloon/granule interactions. I knelt down on the turf, probably causing many confused looks among the other parents, and watched the granules appear to fly upward. It was cool sight to see. As I guided the balloon along the turf, a couple of centimeters above the surface, I could see the granules bouncing along the turf and flying up toward the balloon. Very cool!
So what can you do? Blow up a couple of balloons and let your kids see what they can do with static electricity. Rub the balloons on your hair, clothes, carpet, etc. What works best for building up charge? Which surfaces do the balloons stick best to once charged? Science in action!