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Ball that doesn’t quite seem to come out

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

  • Remove the polystyrene foam ball from the tube with the wind from a hair dryer. A hollow ball with a diameter of 10 cm was used. The tube diameter (inner diameter) is 11.4 cm, and the depth is 30 cm.
  • Aim at the center and blow the wind to lift the ball. The principle is the same as "Remove a ball or egg from the tube".
  • The lifted ball attempts to jump out of the tube, but does not. This is the same principle as "A Stroll with a Ball" and "Supporting a Ball with a Stick". When the ball is about to go out, the air flow hits the side closer to the center of the tube. This stream bends along the ball and flows away (to the left in the figure). Because of this reaction, a force acts on the ball to the right, that is, in the direction returning to the center of the tube, and the ball does not jump out.
[Keywords] Momentum theory, pressure
[Related items] Remove a ball or egg from the tube, A Stroll with a Ball, Supporting a Ball with a Stick

“Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P200-201

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Last Update:3.3.2017