Three One-Yen Coins

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What type of experiment is this?

Experimental procedure and explanation:

• Float three one-yen coins on water.
• Drip one drop of neutral detergent in the middle of the three coins. When this is done, the one-yen coins spread apart in a scattered manner.
• The surface tension of the water near the center is weakened by the neutral detergent, and the difference with the strong surface tension at the outer locations causes the one-yen coins to spread out. The neutral detergent works as a surfactant.

[Keywords]	surface tension
[Related items]	Camphor Boat, Floating Japanese Penny
[Reference]	The Japan Society of Mechanical Engineers, “The Wonders of Flow (Nagare no Fushigi),” Kodansha Blue Backs, pp. 62–67. Ryozo Ishiwata, “Illustrated Fluid Dynamics Trivia (Zukai Zatsugaku Ryutai Rikigaku),” Natsume Publishing, pp. 48–49.