One of my favorite versions: when Steve Jobs immersed an early iPod in water to see if any bubbles came out, and therefore it could be made smaller/tighter.

https://www.google.com/search?q=steve+jobs+ipod+water+air+bu...

Another is when Feynman ducked a piece of o-ring in a glass of ice water, causing it to fail.

https://www.google.com/search?q=feynman+challenger+o+ring