Kids will love this experiment. If it is done correctly, they can make a ball float on air, and it will not fall off.
DO NOT JUST IMITATE THE PICTURE. INSTEAD, FOLLOW THE INSTRUCTIONS SET FORTH BELOW. That Cub Scout up above was lucky. That ball he used is only roughly spherical. Balls which are oddly shaped usually don't work well. Also, he's using one of those elbowing straws. They tend to not work well, because the bent elbow disorganizes the stream of air coming out of the straw.
So, MATERIALS: (1) Styro balls, from one of those arts and crafts superstores; and (2) drinking straws, without elbows, if possible, but if you must have elbowed straws, don't bend them -- keep them straight.
DIRECTIONS: The first time you do this, lay on your back on the floor, put one end of the straw in your mouth, and point the other end of the straw straight up.
Carefully balance the styro ball on the end of the straw.
Take a very deep breath.
Then, NON-explosively blow a steady stream of air onto the ball. It will float up and remain seated, in mid-air, on the column of air.
THE SCIENCE INVOLVED: Air molecules move around like crazy, bouncing off everything in the armosphere, like a trillion, trillion ping pong balls.
This is where air pressure comes from.
When the air from the straw speeds around the smooth sides of the ball, the air molecules in that speeding air don't hit the sides of the ball as well as they used to.
The result is that the pressure of the air on the ball in the speeding air is less.
But, if the ball begins to tumble off and out of the column of speeding air, the air pressure on the ball on the side of the ball touching the still air outside the column of speeding air is much larger, right at that point, knocking the ball back into the speeding column of air.
Thus, the still air, outside the stream from the straw, forms an invisible wall, holding the ball in place.