The reflected pulse in open and closed pipes is slower?

[hellocubed]

---

Members don't see this ad.

When a pressure pulse enters a pipe, it is initially a high pressure pulse. Upon reflection, the pulse returns as a low pressure pulse.


Looking at this equation
http://imgur.com/UpkDZ

There is a clear indication that Higher pressure is associated with higher velocity. From this case it seems that the initial high pressure pulse would be of higher velocity than the second low pressure reflected pulse?

Just wanted to confirm/see if anyone could challenge this...

 

[chiddler]

Upon reflection, the pulse returns as a low pressure pulse.

are you sure about that? where does it say that?

here's what came to mind for me. enters as high pressure pulse, hits end as low pressure pulse, leaves as high pressure pulse. where high pressure means a compression and low pressure means decompression.

 

[hellocubed]

Yes I am sure.

It says verbatim in the BR:

"The pressure pulse that is reflected into the pipe is a pulse of decreased pressure, and it travels back to its origin."

 

[chiddler]

then i don't know. sorry.

 

[SaCkO]

When a pressure pulse enters a pipe, it is initially a high pressure pulse. Upon reflection, the pulse returns as a low pressure pulse.


Looking at this equation
http://imgur.com/UpkDZ

There is a clear indication that Higher pressure is associated with higher velocity. From this case it seems that the initial high pressure pulse would be of higher velocity than the second low pressure reflected pulse?

Just wanted to confirm/see if anyone could challenge this...

Yes it is true .. look at the picture that chiddler posted..where ever you see a node for the wavelength is is a maximum (antinode) for pressure

 

[syoung]

http://www.phys.unsw.edu.au/jw/flutes.v.clarinets.html#time
this explains it nicely.
For closed/open pipe, enters high, reflects high, reflects low, reflects low (1 cycle)
For open/open pipe, enters high, reflects low (1 cycle) there is 180 phase change at each end of reflection

 

[hellocubed]

Yes it is true .. look at the picture that chiddler posted..where ever you see a node for the wavelength is is a maximum (antinode) for pressure

http://www.phys.unsw.edu.au/jw/flute...nets.html#time
this explains it nicely.
For closed/open pipe, enters high, reflects high, reflects low, reflects low (1 cycle)
For open/open pipe, enters high, reflects low (1 cycle) there is 180 phase change at each end of reflection

I think you guys may be missing the question...
We have already established that it goes High, low, etc.


The question is whether the first high pressure length of the wavelength goes FASTER due to the equation I posted (Higher pressure--> higher velocity).

 

[syoung]

here look at this one which is nice with colors.
http://www.phys.unsw.edu.au/jw/flutes.v.clarinets.html
OPEN ends have LOW pressure (because its near atm pressure), closed ends have HIGH pressure (because they have room to oscillate). OPEN ends have HIGH displacement of air or antinodes and CLOSED ends have LOW displacement of air or nodes

 

[chaser0]

Wait, aren't you just repeating what hellocubed is saying?

 

[hellocubed]

Perhaps you should reread my original post?

There is a clear indication that Higher pressure is associated with higher velocity. From this case it seems that the initial high pressure pulse would be of higher velocity than the second low pressure reflected pulse?

Just wanted to confirm/see if anyone could challenge this...

i already know that the wave enters with a higher pressure, and then reflects with lower pressure.
This has been established.


i am asking if the initial high pressure wave travels FASTER than the lower pressure wave.

 

[ipodtouch]

here look at this one which is nice with colors.
http://www.phys.unsw.edu.au/jw/flutes.v.clarinets.html
OPEN ends have LOW pressure (because its near atm pressure), closed ends have HIGH pressure (because they have room to oscillate). OPEN ends have HIGH displacement of air or antinodes and CLOSED ends have LOW displacement of air or nodes

It should also be noted that this is Wrong.
The low pressure and high pressure of a tube has nothing to do with a "side of the tube."

If you read this website
http://www.phys.unsw.edu.au/jw/flutes.v.clarinets.html


In open tubes:
The wavelength that enters the tube originally is propagated with high pressure, and becomes a low pressure wave when it reflects off the end of the tube. Both low and high pressure waves travel the entire length of the tube.

in closed tubes:
The wavelength enters the tube originally with high pressure and reflects off the end, still as a high pressure wave. When it comes back to the origin, it reflects off the origin and travels back down the tube as a low pressure tube.




For OP's question, i am not quite sure. I believe that high pressure and low pressure wave are both traveling through an identical pressure "medium," and hence should have the same speed? I understand that one wave is composed of higher pressure, but I don't believe that's quite the same as traveling through a medium of higher pressure...

Correct me if I'm wrong

 

[chiddler]

Why don't we think of this in terms of bernoulli's.

A high pressure indicates that there is low velocity. A low pressure indicates higher velocity.

edit: wait, no this is wrong because it refers to movement of the fluid (air) which is not relevant. in that case, sure. OP is probably right. Why not?

If anybody understands the mechanism of phase change in a reflecting air pipe, I would love to know.