Why does hot water sound different from cold water?

Question

When pouring hot water out of a kettle it sounds different just after it's boiled, from when it's cold... why is this?

Answer 1

I'll refer you to my answer from a previous version of this question:

http://answers.yahoo.com/question/index;...

Answer 2

Thanks for asking this question; I had never thought about it before and was very fascinated with Lithi's answer.  It still leaves me wondering, however, how much of a difference a little steam in the cup would make on muffling the sound.  The steam around the space shuttle is pretty thick--but it's a pretty small amount in a coffee cup, relatively speaking (you can't even see the space shuttle through the steam cloud, but in my coffee cup, I can hardly see the steam).  

I'm now wondering if there is an additional effect.  Water vapor is less dense than air, so the speed of sound is higher.  With room temperature water the vapor pressure and associated humidity is low compared to the atmosphere, but with boiling water, the air could locally be mostly water vapor.  If you check the speed of sound in water vapor at 100C versus air at room temperature, the speed of sound is 440 versus 346 (see link below).  Any sounds produced under the hot vapor would get compressed moving into air and would sound higher, proportional to the change in speed of sound.  It's the same effect as when you talk when breathing helium.   Could you try pouring a cup of water in a cup while spraying helium in the cup and see if you get a similar effect?  Could this frequency effect be combining with the dampening effect of aerosolized water droplets (not to be confused with vapor).

Answer 3

It is also related to the density of water, as cold water is more dense than hot water.