Using a hair dryer to levitate a ping pong ball is a classic do it at home science experiment. It utilizes two basic principles to keep the ball hovering in the air. The first principle is the transfer of momentum from the moving air particles to the ping pong balls. Basically, the moving air hits the ball and exerts a force upwards on the ball. This is fairly intuitive straightforward. Bernouli’s Principle is the law responsible for keeping the ball contained in the airstream and it is much more complex and interesting.
Bernouli’s principle states that the faster a fluid or a gas move around an object, the less pressure they exert on it. What this means for the ping pong ball is that as the air moves around it, there is less pressure pushing on it from the sides. However, if the ball tries to leave the airstream (because of the collisions from the moving air or due to gravity) it will encounter some stationary air that exerts a higher pressure back on the ping pong ball. Essentially the ball is encountering a wall of static air that bounces the ball back into the airstream. Now because the wall is made of air it doesn’t take too much force to break the barrier, but as long as you keep the hair dryer fairly steady you should be able to keep the ping pong ball levitating for a while. Sadly there were no hair dryers back in Bernouli’s day, but we’d like to think he would have fun with this experiment if he did. Enjoy!