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1 .This is Scientific American's 60-Second Science. I'm Wayt Gibbs. Got a minute?
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2 .British physicist Lord Rayleigh is best known for his discovery of argon and for explaining, in 1871, why the sky is blue.
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3 .But he also puzzled over this:.
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4 .Rayleigh knew that a kettle makes that sound when steam jets through the hole in a thick lid that has a gap in the middle.
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5 .He speculated that the jet becomes unstable inside that gap, setting up an acoustic feedback loop within the gap.
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6 .But he couldn't prove it.
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7 .Now two engineers at Cambridge University claim to have solved the puzzle and proved Rayleigh wrong.
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8 .The work is in the journal Physics of Fluids.
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9 .The engineers found that a kettle actually whistles in two distinct ways.
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10 .It starts off with air vibrating in the gap between the layers of the lid, like when you do this and this.
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11 .But as the pressure builds, vortices of steam peel off from the jet exiting the lid.
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12 .Each vortex creates sound waves at a frequency that depends on the length of the spout and the pressure inside it.
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13 .Rising temperature means rising pressure, which produces a rising whistle.
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14 .Which means it's time for tea.
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15 .Thanks for the minute, for Scientific American's 60-Second Science. I'm Wayt Gibbs.
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