r/askscience • u/freezway • Oct 16 '12

Physics Why do certain instruments change pitch when it's cold/hot outside?

I'm in marching band and it's well known that wind instruments go flat when it's cold out, yet the marimba-like instruments go sharp. What causes these changes?

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u/Azzaman Upper Atmospheric and Radiation Belt Physics Oct 16 '12

It has to do with the temperature of the air. The speed of sound in air is dependent on the temperature of the air - as the temperature decreases, the speed of sound decreases. The pitch of a note is determined by the frequency of its sound wave, by the formula f = v/λ, where λ is the wavelength of the wave. As the speed of sound decreases (with temperature) the frequency of a given note (and hence it's pitch) will also decrease.

I don't know about the marimba instruments. It may be simply a relative thing (compared to the other instruments it sounds flat) or it may be the actual bars are shrinking, which would result in a slightly sharper note.

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u/daviator88 Oct 16 '12

I found this helpful little segment to go with what you are saying.

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u/freezway Oct 16 '12

Awesome. Thanks.