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Removing a Ball from a Cylinder

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Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

  • Use air blown from a dryer to eject a ball that is at the bottom of a measuring cylinder.
  • When the flow of air hits the ball from the top, the ball begins to float upward. This is the same condition as that in “Floating an Egg.
  • When the ball is at the bottom, the trick is to create a flow of air along the wall of the measuring cylinder so that the air passes through the gap together with the ball. At the place where the flow changes its direction and returns, the pressure increases, and overall, the pressure of the air on the downward side increases further. The difference in the pressures between the upper and lower sides of the ball causes the ball to float upward.
  • Once the ball has risen to as far as the middle, it is more stable to apply the flow of air directly to the middle of the ball. By doing so, the ball can be skillfully raised.
[Keywords] momentum theory (law of momentum), pressure
[Related items] Floating an Egg, Force when Flow is Pushed Back, Removing a Cup from a Cylinder
[Reference] “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natume Publishing, pp.200-201

 

Last update: 1.21.2015