# Why Does Sound Propagate?

Discussion in 'Mathematics and Physics' started by crashsite, Dec 30, 2008.

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1. ### crashsiteBanned

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Clarification

No, it's not "philosophy" to me. Your comment regarded me saying that me being right or wrong was moot. Poor choice of words. I should have said that whether I am right or wrong, it's more important to say what I feel needs to be said rather than not saying it. I'd rather post an opinion and be proven wrong than not post it and just keep thinking that I'm right.

In fact, there have been times in this thread that I've said wrong things. Usually when trying to make sense of what the general community thinks (when I really should know better).

Last edited: Oct 19, 2009
2. ### smanchesNew Member

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Wouldn't it depend on how much pressure the air has already? And isn't pressure of a gas directly related to it's current energy level? Doesn't sound travel at different speeds depending on the density of the air? Why do you think that is?

Last edited: Oct 19, 2009
3. ### crashsiteBanned

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Lots of Variables

Okay, that's one of the "sticking points" to this whole sound propagation thing. The answer is, "no". The speed of sound does not depend on the density of the air. But, it does depend on the energy in the air (more specifically, heat energy). The heat energy is manifest by how fast the molecules will be moving.

That's a very key point to sound propagation. The speed of sound is directly related to the speed of the molecules and the speed of the molecules is related to the temperature. Any theory of sound propagation cannot violate that.

The practical effect is that, once the medium has been established, only the temperature determines the speed of sound through it. I'm not sure what happens during extreme conditions. For example, if you have steel, the speed of sound is about 13,000 mph. But, if that steel becomes molten or what if it's work-hardened and becomes crystalized? What effect does that have on the speed? I don't know. Maybe someone here does.

But, as to how fast the air will be 'sucked' into a void, that's a question of moving an air mass and a whole different set of rules applies. I suspect that the massiveness of the air (density) and pressure probably do change the speed at which that happens.

The pressure of a gas is related to the temperature (at least in an enclosed space) but, you still have to be careful of what you are talking about. That's a factor that makes this subject so tricky to discuss. Are you talking about static pressure or moving air or propagating sound or creating a pressure differential or making waves or some combination?

In this thread, I've tried to zero in on just how sound propagates (more specifically, in air).

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5. ### Nigel GoodwinSuper ModeratorMost Helpful Member

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OK, this thread is the longest running on these forums, and has the least content - it's mostly just a blog for the OP, for his vivid imagination.

As such it's now closed, and will be deleted in the next few days.

If you want to run a blog, then set your own site up.