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When the plastic bottle is upside down

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What type of experiment is this?

Experimental procedure and explanation:

  • Fill a plastic bottle with water, turn it upside down, and stand it in the water of the aquarium. The water in the plastic bottle does not flow out.
  • At this time, in the plastic bottle, the atmospheric pressure is at the same height as the surrounding water surface, and the air pressure at the top is lower than the atmospheric pressure because of the height of the liquid. The force caused by the pressure difference between the top and bottom can balance the weight of the liquid and support the weight.
    (Difference in vertical pressure) = (Density of liquid) × (Gravity acceleration) × (Height of liquid)
  • The plastic bottle used in the experiment is 2 L, so the water inside weighs approximately 2 kg. What is supporting this weight is the force caused by the vertical pressure difference.
[Keywords] Depth and pressure
[Related items] Scoop liquid with a straw, Water that Won't Overflow

“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, P38-41.

“Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P18-19.

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Last Update:3.3.2017