Trapping a Ball

Let's take a look!

Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

• Make a diffuser section in front of a dryer using a funnel.
• Using this setup, blow air to levitate a styrene foam ball (10-cm diameter, hollow).
• Then, place your hand over the ball to manipulate the height of the ball.
• Lower your hand to trap the ball in the funnel.
• The ball will not fall off, even when the dryer is tilted to its side.
• Placing your hand adjusts the wind strength, and this is how you are able to manipulate the ball height.
• The ball is trapped because the gap between the ball and the funnel is smaller, thereby increasing the flow speed and lowering the pressure.
• This is the same principle used in racecars in which a downward force (negative lift) is created by lowering the floor (ground effect).

[Keywords]	Bernoulli’s theorem
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Koudansha Blue Backs, pp. 102-107 “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, pp. 136-137