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What weighs more: a cup of water filled to the brim or that same cup of water, also filled to the brim, with a piece of wood floating in it? Why?
- Ellie (age 15)
Nice question: it makes you think. The answer is they weigh the same because the floating wood displaces an amount of water equivalent to its own weight. That's what Archimedes figured out a long time ago. This displaced water dribbles down the side of the glass. The remaining water plus the weight of the wood add up to the amount of the water only case.
(published on 10/09/2011)
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