Container and Lid 1 (Something Happens with a Countdown)

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• Cover the empty can with a plate, submerge the can in water, and release your hands. The plate stays in place and nothing happens.
• Then, a countdown begins. When it ends, the plate suddenly comes off.
• The secret lies in the small hole at the bottom of the can.
• Initially, if you cover the hole with your finger, the air pressure inside the can remains close to atmospheric pressure. This internal pressure pushes upward on the underside of the plate. Meanwhile, water pressure—greater than atmospheric pressure due to water depth—pushes downward on the top of the plate. Since the pressure from above is stronger, the plate stays pressed against the can and does not fall.
• When the countdown ends and you remove your finger from the hole, the air pressure inside the can changes to match the pressure at the bottom of the can. As a result, the pressure pushing up from inside becomes greater than the pressure pushing down from outside, and the plate is lifted.
• This video was produced with the support of the JSPS Grant-in-Aid for Scientific Research (18K03956).

[Keywords]	Depth and pressure
[Related items]	The Bowls that won't come Apart 2
[References]	The Japan Society of Mechanical Engineers, “The Wonder of Flow,” Kodansha Bluebacks, pp. 38–41. Ryozo Ishiwata, “Illustrated Fluid Dynamics Trivia,” Natsume Publishing, pp. 18–19.

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