Container and Lid 4 (Lid is Lighter than Water)

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• Cover the hole at the bottom of the can with vinyl tape, and drill a small hole in the plate.
  In this video, a Styrofoam plate, which is lighter than water, was used.
• First, cover the hole in the can with your finger and submerge it with the plate facing upward.
• When the finger is released, the plate floats up.
• The air pressure inside the can and the water pressure outside the hole are nearly equal. As a result, the forces acting on the top and bottom of the plate are balanced.
• In this case, the plate floated because it was lighter than water.
• Note that the hole in the plate is small, and surface tension at the water–air interface prevents water from entering through the hole.
• Next, cover the hole with your finger and submerge the can with the plate facing downward.
• When the finger covering the hole is released, the plate remains in place and nothing happens.
• The air pressure inside the can and the water pressure outside the hole are nearly equal. As a result, the forces acting on the top and bottom of the plate are balanced.
• In this case, the plate remained pressed against the container because it was lighter than water.
• This video was produced with the support of the JSPS Grant-in-Aid for Scientific Research (18K03956).

[Keywords]	Depth and pressure
[Related items]	Container and Lid 1
[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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