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Force When Flow is Pushed Back

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What kind of experiment is this?

Experimental procedure and explanation:

  • Place a bowl with a flat plate on top of it onto a scale and blow on it from above with a dryer.
  • When the air initially hits the flat plate, the flow is blocked; thus, the pressure on the surface of the plate increases, and a downward force acts on the plate. Before blowing air onto the plate, negate the weights of the bowl and the plate by pressing the reset button on the scale until the display shows 0 g.
  • Next, remove the plate. When the flow of air hits the bowl, the flow of air is not only blocked but also pushed back. As a result, the pressure on the bowl surface increases even more than in the case of the plate. The force acting on the bowl also becomes larger than that acting on the plate. Before blowing air onto the bowl, press the reset button on the scale until the display shows 0 g.
[Keywords] momentum theory (law of momentum), pressure
[Related items] Floating an Egg
[Reference] “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natume Publishing, pp.200-201

 

Last update: 1.21.2015