Why Does Sound Behave Differently in Various Gases and Media?

[McKeavey]

Homework Statement

If light travels forever in space..Why does sound die off in air?

When a person inhales helium, his voice sounds high. There is another gas when you inhale it, your voice sounds low.
How does this effect work..?

Does a music note of frequency 440Hz have the same wavelength in water as it does in air?


2. The attempt at a solution
The waves span out..? No idea.

Magic?

No, because it doesn't travel through the same medium..?

Thanks for answering!

 

[Delphi51]

Call the questions a, b and c.
I think you may have the idea of (a), but the word "span" is not very clear to me.
You must play with (b) a bit. How would you say "sounds high" in physics terms?
Good start on (c). Now what is different about the two media that affects the sound waves? Again, looking for a physics term whose value is different in the two media.