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Floating an Egg

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What kind of experiment is this?

Experimental procedure and explanation:

  • Place an egg in a cup and fill the cup with water. When the cup is filled vigorously with water, the egg floats upward.
  • The flow is blocked at the point where water from the faucet hits the egg (point A), resulting in the increased pressure.
  • The water then flows along the egg. Near point B, the vertical direction is changed, and water flows upward. The flow momentum is stopped at point B, and a pressure larger than that at point A is generated to push the flow back.
  • Because the pressure at point B is large, the pressure under the egg becomes larger overall. This pressure is larger than the pressure above the egg, because which the egg is lifted upward.

[Attention] Some scientific books use Bernoulli’s principle to explain the theory that causes the egg to float upward. However, it is a mistake. This is based on the pressure of the water flowing along the egg becoming smaller, but the impact of the increase in pressure at the point where water from the faucet hits the egg (point A) is greater; therefore, the egg would only be pushed downward. Hence, this principle does not agree with the facts.
[Keywords] momentum theory (law of momentum), pressure
[Related items] Force When Flow is Pushed Back
[Reference] “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natume Publishing, pp.200-201


Last Update:1.21.2015