Water that won't fall (pull up cup)

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What type of experiment is this?

Experimental procedure and explanation:

• Submerge a cup in a filled water tank and turn it upside down.
• Next, put the lid on it. Next, press the lid firmly upward to keep it in contact with the cup. This is to ensure that the water pressure inside the cup is less than the water pressure outside of the cup when it is pulled up. If you do not do this, the lid will come off, and the experiment will fail. The board should be slightly deformed.
• If you pull up the cup slowly, you can take it out of the water without removing the lid.
• Surface tension does not work when the rim of the cup is submerged in water. This is because both the inside and outside are water, and no interface is formed.
• The force that keeps the water in the cup even when the cup is being pulled up is the pressure difference between the top and bottom of the water in the cup (= water density × gravitational acceleration × height).

[Keywords]	Depth and pressure, surface tension
[Related items]	Water that won't fall, When the plastic bottle is upside down
[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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