- Molecules are displaced vectorX in meters in a sound wave. - With starting velocity in direction of vectorX of molecular drift velocity component agreeing with vectorX - Ending velocity of some amount vectorV - Due to net force vectorD causing - Acceleration vectorA
How do we determine the restorative force acting on the displaced molecules of air in a sound wave, and what source does this force(s) have?
By restorative force, I mean that force which is generally called the "rarefaction portion of a wave".. You can't have negative pressure!
Is it exactly equal and opposite the displacing force vectorD (originally due to driver movement)?
If so, then how do external forces sum to exactly that of the driver force on air?
Note: Rarefaction forces aren't due to a low pressure area pulling things. They're due to a higher pressure area PUSHING things into the lower pressure areas. One can't say simply that because the driver creates a low pressure area with its motion that that will BE the restorative force, rather, that will allow some other part to exert the restorative force.
So, how does the rarefaction portion of the wave work?
ShadowStar
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Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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I am not familiar with all of the terms you used but this is how I see it:
When the cone moves forward it moves the air with it, which, if the cab is solid, makes the given amount of air fit into a smaller space, compressing it. On the back stroke of the cone the area that the cone makes available to the air has lower pressure than the rest, and the high pressure forces air into the low pressure area in front of the cone (as you stated). What I think you are looking for is the "spring" of the air (its tendency to move easily from one level of pressure to another). I don't exactly know the term for this, or why it occurs. And when you say there isn't such a thing as negative pressure, there isn't on the back stroke of the cone, there is just less than the pressure that we live in (~14 psi I think), but when you hit 193 db that changes. What exactly happens at that level I don't know, and couldn't even begin to predict. Am I on track? Or just repeating what you said in different words?
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[This message has been edited by Rybaudio (edited 04-06-2001).]
Posts: 3956 | From: State College, PA | Registered: Sep 2000
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Thats what happens at 193 db, ryb.. The back stroke "low pressure" approaches 0 psi, creating a total vaccuum.. Thats pretty hard to do
The air molecules themselves are trying to live with an overall space change, yes.. But displacement of the driver compared to the total air to be displaced is a pretty small ratio!
But, the displacement of the driver causing a pressure change is sort of a macroscopic view of what I'm trying to examine on a molecular level. For most intents and purposes that explanation works, but I'm building up some theory
ShadowStar
------------------ Still looking for that CHEAP Thunderdome :D
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Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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