Floating Ping Pong Ball
Concepts: The Bernoulli effect
1. Turn on the hair dryer and hold it so that the stream of air is pointing up at the ceiling.
2. Place the ping pong ball in the stream of air.
3. Further demo: Take a 1-2 inch wide x 11 inch long strip of notebook paper. Let the strip flod over your fingers and hang down. Now bring the slip of paper close to your mouth and blow across the TOP of the strip. If done correctly the strip of paper should rise in the air. This may be contrary to what you expect might happen.
Explanation: You have just witnessed a really wacky demonstration of the Bernoulli effect, and its the same princliple that allows heavier than air objects like airplanes to fly. Moving air exerts less pressure in a direction at right angles to its motion than still air does. Since the air stream from the hair dryer moves faster around the side of the ball (and thus exerts less pressure) than the still air on top of the ball, the heavier air pressure on top of the ball holds it firmly in mid air.
These principles are also shown with the demo with the strip of paper. As fast air rushers over the top of the paper, there is less pressure on the top of the paper. Thus the higher pressure air on the bottom of the strip causes the strip of paper to rise.
Airplanes can fly because of this principle. Air rushing over the tops of airplane wings exerts less pressure then air from under the wings. So the realatively greater air pressure beneath the wings supplies the upward force, or lift, that enables airplanes to fly.