I love this science project from Filth Wizardry. She shows how to put together a kid-friendly contraption that demonstrates the Bernoulli Effect.
So, the column of air coming from the hairdryer is moving fast, hence has a lower pressure than the surrounding air outside of the stream from the hairdryer. When you place the ping pong ball in the stream of fast moving air, it is held there by the higher pressure pushing on it from all around outside the stream. This means you can even tilt the stream of air and the ball will stay in it, which just looks weird and totally freaks the kids out. Magic? No! Science!