What happens

The demonstrator uses Bernoulli's principal to make a beach ball hover in the air above a leaf blower. The patterns of air flow around the spherical beach ball keep the ball in place above the leaf blower.

How it happens

Bernoulli’s principle states that fluids in an area moving faster than the the surrounding area possess less pressure. (In general, fluids include liquids and gasses. Air is a gas and as such is classified as a fluid.) 

To explain this demonstration a good understanding of the Bernoulli effect along with terminal velocity is required. The ball is held up by the wind blast putting the ball at it’s terminal velocity. The ball moves up if the wind is faster than terminal or moves down towards faster air if the air speed is less than terminal velocity. The ball will always settle in at the right point where terminal velocity air is moving up and flowing around the ball.

The bigger question is why the ball stays centered in the stream of air? The air in the center of the air stream will be moving a little faster than the air towards the edge. This is due to the fact that the air at the sides rubs on the stationary air in the room and is slowed a little. If the ball begins to drift off center the faster air passing the ball will be on the side back towards the center. In Bernoulli faster air produces less pressure and the larger pressure (slower air) on the outside will cause the ball to be recentered. If you watch the ball you can see it being recentered almost all the time.

Vocabulary

air pressure: Pressure exerted by the weight of air on an object in that air. 

atmospheric pressure: This is also the pressure caused by air, but usually thought of as the normal value or standard value of 14.7 pounds per square inch. The atmospheric pressure at the place where we are on the face of the earth is usually less than this because we are above sea level, and hence have less "weight" pushing down on us. 

high pressure: A space where the pressure is more pounds per square inch than a neighboring space. 

low pressure: A space where the pressure is fewer pounds per square inch than a neighboring space. 

molecular motion: The name given to the intrinsic property of all matter that is at normal temperature where the molecules of that matter are in a constant state of motion. We will be using this concept to help describe what causes air pressure. 

pressure: In the context of our show, it will be the number of pounds per square inch exerted by gaseous molecules. When the number of pounds per square inch are multiplied by the number of square inches on an object, it is possible to determine the total force, the push on the object.

terminal velocity: Terminal velocity is the highest velocity attainable by an object as it falls through a fluid. It occurs when the sum of the drag force and the buoyancy is equal to the downward force of gravity acting on the object.