Sound Waves

[MedPR]

"Note that as the waves move outward, there are regions of high density and low density within the medium. Also note that the volume of space associated with the regions of high density decreases relative to the volume of space associated with the regions of low density"

I'm not seeing that in the figure. It makes sense that as waves propagate away from a source (basically a single point in space) that the regions of high density get smaller since the area they have to spread out gets larger. Kind of like spraying water out of a spray bottle.. The stream starts out really small then disperses into a wide cone shaped thing. Is this the concept the text is explaining, and just not showing in the figure?

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[milski]

I am not sure what they are trying to get to here. The distribution of the pressure follows a regular sinusoide. The only way to get the graph in the attached picture is to call 'rarefaction' any pressure that is not high enough to be in the peaks. From that point of view, you can tell that the high pressure is in narrower bands compared to the rarefied air.

As the air waves spread away both the highest pressure will go down and the lowest pressure goes up. The compression/rarefaction will stay symmetrical to the ambient pressure.

 

[silverice]

I am not sure what they are trying to get to here. The distribution of the pressure follows a regular sinusoide. The only way to get the graph in the attached picture is to call 'rarefaction' any pressure that is not high enough to be in the peaks. From that point of view, you can tell that the high pressure is in narrower bands compared to the rarefied air.

As the air waves spread away both the highest pressure will go down and the lowest pressure goes up. The compression/rarefaction will stay symmetrical to the ambient pressure.

I have the exact same question. Do they mean the the high density area it's like the antinode of the wave?

 

[milski]

I have the exact same question. Do they mean the the high density area it's like the antinode of the wave?

Sort of but the hight density area is not stationary - it is moving away from the source. Keep in mind that it is the pressure that's moving away, not the particles themselves.

 

[silverice]

Sort of but the hight density area is not stationary - it is moving away from the source. Keep in mind that it is the pressure that's moving away, not the particles themselves.

Oh Right! Thanks for reminding me, it's the transfer of energy but not the particle itself because the pressure or energy is transfer by vibrating the molecule in the medium.