Inside the plywood box is a motor and fan which push air up through the safety cone. The cone acts as a funnel to produce a nice round column of upward air. To understand this exhibit one must realize that the air around us is always exerting pressure in all directions. Thus air is pushing down on our shoulders, up on our chin, in on our chest and in on our back. Air is pushing down on the surface of a table and up on the underside of the table. In still air at sea level this pressure is about 14.7 pounds on every square inch.
Moving air also exerts pressure. However air moving along the surface of an object pushes against the object with less pressure than still air. To demonstrate this, tear off a piece of newspaper about two inches wide by six inches long. Pick up the piece of paper by one corner and hold it in still air. Air is pushing equally on both sides of the piece of paper.
At one end of the strip of paper use a thumb and forefinger to hold each corner. Rotate your hands so that your thumbs and forefingers are horizontal (parallel to the floor). That end of the strip of paper is horizontal but the paper gradually curves towards the floor because gravity is pulling down on the paper. Air is still pushing equally on both sides.
Keeping your thumbs and forefingers horizontal, bring the end of the piece of paper against your lower lip and blow across the top of the strip of paper. The other end rises because the air moving along the top of the paper is pushing down against the paper with less force than the still air on the underside of the paper.
Consider the cross-sectional shape of an airplane wing. The underside of the wing is flat. The upper side of the wing is higher in the middle than at the front and back edges, meaning that the top of the wing is curved. Pretend that there are two ants on the front edge of the wing. They are each going to walk to the back edge of the wing, but one is going to walk along the flat underside of the wing and the other along the curved upper side. The distance the upper side ant must walk is longer than the distance the underside ant must walk. If they are to arrive at the back edge at the same time the upper side ant must walk faster than the underside ant.
As an airplane flies the front edge of the wing is a divider, forcing some of the air to move along the underside of the wing and some along the upper side. In order to keep from piling up in front of the wing, the air moving the shorter distance along the underside of the wing must get to the back edge of the wing at exactly the same time as the air moving the longer distance along the upper side of the wing. Therefore the air moving along the upper side of the wing must move faster than the air moving along the underside of the wing.
As shown when you blow across the top of a piece of newspaper, moving air exerts less sideways pressure than still air. Similarly, faster moving air exerts less sideways pressure than slower moving air. Therefore an airplane flies because the faster moving air along the upper side of the wing pushes down with less pressure than the slower moving air along the underside of the wing.
In this exhibit, when one of the balls is inserted part way into the upward column of air, there is fast moving air on the inner side of the ball and slow moving or perhaps still air on the outer side of the ball. This fast moving air exerts less sideways pressure on the ball than the slow moving or quiet air. Therefore the ball is pushed into the air stream by opposing unequal air pressures. Air in the center of the column is moving upward faster than air near the outer edges of the column.
Push lightly on a ball floating in the column of air and what happens? Why does the ball return to the center of the column of air? Again, when the ball is not in the exact center of the column then air is moving upward faster on one side of the ball than on the other, creating unequal sideways pressures. These unequal pressures return the ball to the center of the air column.
Attach a penny to one side of a ball using cellophane tape. Notice that the ball now is less stable because it demonstrates an irregular pattern of rotation. What would happen if a second penny were taped close to the first? On the opposite side of the ball from the first?
Use cellophane tape to create one or two small flaps on the surface of a ball and put it into the air stream. Sometimes the ball will begin a stable rapid spin, and other times the ball will maintain an irregular spin.