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Why does sound travel faster in humid air?

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August 10, 2008 5:52PM

Sound will travel a little bit faster in humid air (about 0.1% to 0.6% faster) than it does in dry air. Follow along and we'll see why. Air is mostly nitrogen and oxygen. Nitrogen and oxygen travel around with "buddy" atoms - they are diatomic molecules - they are N2 and O2. Humid air contains water molecules, little H2O molecules. The H2O molecules are lighter than are the N2 and O2 molecules they will displace in air. And "lighter" gases carry sound faster than "heavier" gases. Helium will transmit sound faster than "regular air" will. (The rule of thumb is that low molecular weight gases transmit sound faster than higher molecular weight gases.) That's it in a nutshell. Wikipedia has an article on the speed of sound where this and other questions similar to it are answered. Read that article and you'll be 0.6% to 0.7% smarter. (Possibly.) You need a link, and because this is WikiAnswers, we got one for you.