Closed pipe

[yellowjellybean]

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Hey guys, I'm having a hard time understanding this explanation from tbr.

A closed pipe cannot vibrate twice the fundamental frequency. Why? If we were at twice the fundamental frequency, then a pressure pulse would have traveled to the closed end of the pipe and back to the open end before another pulse could be initiated. Recall that the pressure pulse was inverted as it came off of the closed end of the pipe. If this inverted pressure pulse encounters a new pulse, there will be destructive interference.

How could it destructively interfere with another pulse if it travels to and back before another pulse can be initiated?

 

[DrknoSDN]

I am probably misunderstanding but... Wouldn't twice fundamental frequency cause a new pulse to be initiated as the first wave was impacting the closed end of the pipe?
Why would the first one reflect and exit the open end before a new wave was generated? Twice fundamental frequency means they are occurring more often than required, not less often.

Sorry if I completely misunderstood. =/

 

[SpaceBuff12]

This site has some nice animations to describe longitudinal waves in a pipe:
http://www.acs.psu.edu/drussell/Demos/StandingWaves/StandingWaves.html

On why you cannot have even multiples of the fundamental frequency: think of the boundary conditions of a closed end pipe. What conditions must occur at the boundary both in terms of pressure and particle displacement? If you are plotting the variation of pressure along the pipe then it makes sense that the pressure of the closed end of the pipe can oscillate but the pressure at the open end of the pipe must be equal to atmospheric pressure at all times.

 

[DrknoSDN]

Veritasium gives us probably the most amazing video you will ever watch that is directly related to this post. [trust] (3:38 for more-awesome.)

 

[yellowjellybean]

This site has some nice animations to describe longitudinal waves in a pipe:
http://www.acs.psu.edu/drussell/Demos/StandingWaves/StandingWaves.html

On why you cannot have even multiples of the fundamental frequency: think of the boundary conditions of a closed end pipe. What conditions must occur at the boundary both in terms of pressure and particle displacement? If you are plotting the variation of pressure along the pipe then it makes sense that the pressure of the closed end of the pipe can oscillate but the pressure at the open end of the pipe must be equal to atmospheric pressure at all times.

Thanks for the link. That page was so helpful!