Water that won't fall (on a board with a hole)

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What type of experiment is this?

Experimental procedure and explanation:

• Fill a cup with water and cover it with a board that has a hole (about 2 mm in diameter). Even if this cup is turned upside down, the water will not fall. (The hole was made in the plastic board using a pin vise.)
• If the hole is small, the surface tension helps maintain a pressure difference between the inside (water) and outside (air) of the hole. If the hole is large, the interface between the water and air cannot be maintained and the lid will come off, and the water will flow out.
• The force that keeps the water in the cup is the pressure difference between the top and bottom of the water in the cup (= water density × gravitational acceleration × height).

[Note]	Please be careful not to hurt yourself when creating a hole in the board. Please do this with the help of an adult.
[Keywords]	Depth and pressure, surface tension
[Related items]	Water that won't fall
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, p. 38–41 and p. 62–67. “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, p. 48–49 and p. 18–19.

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