Helium answer from 2000

The answer seems reasonably complete, but you may want to add an explanation concerning the speed of sound in various mediums. People remember from science class that sound travels more quickly in more dense materials, thinking of examples given using solids. The article states that helium is less dense and so sound moves more quickly.

The whole business of speed of sound in various materials is a little more complex than just density it seems, looking over the various equations on wikipedia.

Check out the recent back and forth on Wired:

The column in question is Why does helium make your voice squeaky? (14-Jul-2000).

Just to clarify, sound travel faster in *stiffer * materials, and slower in *denser * materials.

Whether or not people in general *think * that sound travels more quickly in denser materials I do not know. I imagine some people do, but “some” people will believe anything.

Sure, some people will believe anything, but I’m not talking about faith healing or UFO research or cryptozoology.

I’m talking about mistaken belief based on past science instruction. You will note in that Wired article comment section someone says “You are wrong in your explanation because I was taught that denser materials transmit sound faster.” This caused to to examine several sources to arrive at a better understanding.

Wikipedia states the case like this:


It’s that last paragraph I’m talking about.
What I am saying is that I saw an example of what I believe will be a common objection to your explanation. If anyone believes it is important enough, I suggest adding more information to that explanation.

An interesting thought. The problem is that Alphagene no longer writes Staff Reports, and the energy and effort involved in revising an eight-year-old report is more than it’s worth.

If we have a volunteer to write an addendum, I’ll be glad to consider it.