This scale balances a cup of water with a certain weight. Will the balance be upset if you put your finger in the water, if you’re careful not to touch the glass?
Yes. The water imparts an upward force on your finger as you immerse it, so you must exert a downward force to overcome it. That force is transferred to the glass and then to the scale, which sinks.
From Yuri B. Chernyak, The Chicken From Minsk, 1995.
November 2, 2012 | Puzzles
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