Bernoulli blower

From WikiDemos

The Bernoulli Blower is a fun demonstration on the principles of flight and, of course, Bernoulli's principle.

Materials

One leaf blower
One or more various inflatable, stuffed, or foam balls

Setup

After all balls are in hand (whether or not after inflating), activate the leaf blower and direct it's air stream straight up into the air. With your other hand, place a ball 2-3 feet above the leaf blower and release. This may take a couple of tries to master, but afterward the ball is suspended due to the constant airflow. Once controlled, try tilting the leaf blower and get the ball to stay suspended a couple of feet outward. If done well, an inflatable ball has the ability to stay in midair several feet away from the leaf blower in the outward direction.

Cheap alternative: leaf blower = your body + straw. Small light balls (I can't remember now what I saw used... ping pong balls?)

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Explanation

This demonstration focuses on the principles of lift. As air must travel faster on the top of the ball than the air under the ball in order to travel around it in the same amount of time*. Faster moving air on the top of the ball creates a lower pressure on the top of the ball (Bernoulli's Principle) and because of this keeps the ball suspended. This same fact is the basis for flight and allows birds and planes into the skies. As for when the leaf blower is aimed strait up into the air, the air passes along all sides of the ball stabilizing it, while a constant flow of air underneath the ball provides the required pressure to keep it afloat.