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February 3, 2012

Strange But True!

Q. Drop a raisin into water and it simply sinks to the bottom and is rather boring. But if you drop it into champagne — for those special times when the celebration requires a raisin or two — it will repeatedly move up and down. Why does this happen?

A. The champagne (or soda or beer) has lots of dissolved carbon dioxide, with some molecules coming together to form bubbles, says Jearl Walker in “The Flying Circus of Physics.” But the bubbles require nucleating sites to form, which can be in tiny crevices on the glass surface or on contaminates lying on the surface or, with the glass of champagne, on the surface of a raisin. As bubbles form and grow on the raisin, they produce a buoyant force large enough to bring the fruit to the surface. But once in the air, the bubbles pop open and release their carbon dioxide and the raisin again sinks to the bottom. This cycle is repeated until the champagne loses most of its dissolved carbon dioxide (goes flat).


 
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