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Removing a Cup from a Cylinder

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Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

  • Use a dryer to remove a cup that is at the bottom of a measuring cylinder.
  • As with “Removing a Ball from a Cylinder,” the trick is to apply the flow of air to the side of the cup. At the place where the direction of flow changes and returns, the pressure increases. However, overall, the pressure of the air at the bottom and inside the cup increases further. The difference in the pressures between the upper and lower sides of the cup causes the cup to float upward.
  • When the flow of air is applied to the center of the cup once it has reached the top, the cup moves downward. This occurs because when the flow of air hits against the bottom surface of the cup, the flow is pushed back in this vicinity. The bottom of the cup receives this pressure overall. This is one of the reasons that the downward force increases.
[Keywords] momentum theory (law of momentum), pressure
[Related items] Removing a Ball from a Cylinder, Force When Flow is Pushed Back
[Reference] “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natume Publishing, pp.200-201


Last Update:1.21.2015