Surgical Operation?

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What type of experiment is this?

Experimental procedure and explanation:

• A copper ball is allowed to sink in a PET bottle filled with water, which we will remove while spilling the least amount of water inside the bottle. We will need tweezers and disposable chopsticks (about 3 cm in length).
• Place a horizontal notch on the side of the PET bottle, and cover it with Cello tape.
• If you tear off the Cello tape first, almost no water spills out.
• Next, widen the cut and insert the disposable chopsticks. Although the water surface is exposed, the water inside does not overflow. This follows the same principle as that in the previously published “Water that Won’t Overflow”.
• If you close the cap tightly, the pressure at the upper part will either be high or low. Meanwhile, if the water surface is exposed on the side, the pressure at the bottom becomes atmospheric pressure, and the pressure at the top becomes lower than atmospheric pressure and is balanced.
• The pressure difference between the top and bottom becomes equal to the density of water × gravitational acceleration × height; this pressure difference supports the weight of the water inside. Therefore, the water does not overflow.
• Insert the tweezers through the open mouth and take out the copper ball present inside.

[Keywords]	Depth and pressure, Surface tension
[Related items]	Water that Won’t Overflow
[Reference]	“The Wonders of Flow”, Japan Society of Mechanical Engineering, Kodansha Blue Backs, P38－41 and P62-67. “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P18-19, P48-49, and P52.

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