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Plastic Bottle with Holes

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What kind of experiment is this?

Experimental procedure and explanation:

  • Prepare a plastic bottle with small holes (1.5 and 5 mm in diameter) on the side. Seal the holes with vinyl tape, pour water into the bottle, and then screw on the cap.
  • The water will not flow out of the hole when you remove the tape. (However, it will flow out through a bigger hole.)
  • If you open two holes, one above the other, water flows out from the bottom hole while air is sucked into the top hole.
  • Water does not flow out of a single small hole because the pressure difference caused by the height difference across the hole (= water density × gravitational acceleration × height) can be supported by surface tension. At this point, the pressure of water at the same height as the hole is almost at the atmospheric level. Even with a 5-mm hole, water does not flow out.
  • When there are two holes, one above the other, the water film has to sustain the pressure difference caused by the height difference between the two. The force of surface tension is not large enough; therefore, the water film breaks and water flows out.

[Keywords] surface tension, depth and pressure
[Reference] “The Wonders of Flow,” Japan Society of Mechanical Engineering, Koudansha Blue Backs, pp. 62-67
“Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, pp. 48-49 and 18-19
Last update: 9.7.2013