Taking out the object that lies at the bottom 2

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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 are a small PET bottle filled with water and a telephone card (other things are also fine if they are solid thin plates).
• Remove the cap of the PET bottle and place the telephone card. Hold the telephone card with a finger and turn the PET bottle upside down. This state is the same as that in the previously published "Water that Won’t Fall”.
• Since the weight of the copper ball is heavy, hold it lightly with your hand and gently place it on the small PET bottle with the cap removed. When you pull out the telephone card, the copper ball will fall.
• Insert the telephone card again and reposition the large PET bottle back to its original state.
• The fact that water did not spill when the large PET bottle was turned upside down is attributable to the same principle as that explained in “Water that Won’t Fall”.
• The pressure on the water surface in the gap with the telephone card is atmospheric pressure. At the upper part (bottom) of the PET bottle, the pressure drops below the atmospheric pressure by an amount that equals “density of water × gravitational acceleration × height.” This creates a pressure difference between the top and bottom inside the PET bottle, which helps support the weight of the water inside. The surface tension keeps the surface of the water from swaying, it does not support the weight of the water inside.

[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, P38－41 and P62-67. “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P18-19 and P48-49.

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