sound waves in pipe

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The representation of sound vibration in pipes is usually this:



since sound is made of longitudinal waves, what does the sinusoidal wave represent?

 

oh

 

Your book should have indicated that's this is indeed not an accurate representation of the sound waves (and changes in amplitude like you just indicated) But you're right! In truth, the top picture should be really shown.

This sinusoidal waves are just drawn for learning purpose--to visually see how many wavelengths fit in the tube.

 

no wait. y axis is not right.

 

Yes, pretty much ΔP.

 

oh

thanks for the help.

 

its graphed as a sinusodal wave as the longitudinal wave creates regions of compression and rarefaction. Regions of compression are crests and regions of rarefaction are troughs.



i guess they got to it first

 

you're wrong. I got to it first ;D

question: why do closed ends of pipes have to contain a node? why do open ends have to contain antinodes?

book says: there is always a displacement node at the closed end (because the air is not free to move) and an antinode at the open end (where the air can freely move.)

if air cannot move shouldn't it be a rarefaction?

NO WAIT a rarefaction indicates air movement. The only one that doesn't indicate air movement is node.

i'm on a roll!

 

thanks for the explanation i was a little stumped by that one.

 

Can you please explain a little more, I'm super confused on this concept.