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# Standing waves in open tubes

Find out  how ​standing waves and resonance cause a flute makes such specific notes. Discover why blowing over a soda bottle creates a tone, how air molecules oscillate in an open-ended tube, and the mathematical representation of these phenomena. Created by David SantoPietro.

## Want to join the conversation?

• If the standing wave does not go to anywhere how we can hear it's sound? In other words, how the wave reaches the ears if it doesn't move?
• What Dave is trying to say is that although the result of 2 waves creates (,or appears to be) a standing wave , just like in the case of propagation of sound , the energy/disturbance is transferred , even if no particle moves from its position. Hope it helps !!
• are standing waves and stationary waves the same ?
• yes, a standing wave, is a stationary wave.
• Hello, sorry, I just have one question. For the green wave you drew, in the second harmonic, how can the point at the middle have maximum amplitude, if the air particles in the middle do not move? I guess what I'm trying to say is that shouldn't the middle of the tube always be a node? Thank you in advance.
• The important part when we are doing the tube question is that if the ends of the tube is open or closed, but the amount of the nodes inside the tubes are dependent on the frequency and the wavelength of the wave. To give you an example it is like a wind instrument, both ends of the tubes (instruments) are open ended, but this does not mean that it can only give off one pitch but dependent on the wavelength and frequency the pitch changes.
• AT
It is said, that the wavelength of that standing wave can be found using the formula
Wavelength (lambda) = 2* (Length of the tube)/ n , where n=1,2,3,.....
But, looking at the graph carefully, we can take n= no. of nodes...
Can'nt we?
• Yes, we can, since the 1st harmonic has 1 nodes, the 2nd harmonic has 2 nodes and so on.

I am having trouble understanding something about the standing wave in the tube open at both ends, at the 2nd harmonic. In this case, the length of the tube "L" equals one whole wavelength.

My question is: shouldn’t there be 2 locations with zero displacement, or "nodes", at exactly 1/4 of the tube’s length from either end? In other words, the left node should be at 0.25*L from the left, and the right node should be at 0.25*L from the right. Correct? One wavelength contains four equally-spaced 90° phases. So I can grip that resonating tube at exactly 1/4 of its length from the top without dampening the vibration.

BUT I have built tubular bells in the past. In all of the literature (and in experience), the correct locations for these two node points is actually L*(0.224), rather than 0.25. Would someone mind explaining this?

I appreciate it!
Tang Bo
• why is it that a node for general displacement is an anti node when in a pressure situation? and an anti node for displacement is a node for pressure as well?

why do they flip? This came up in the unit test question and wasn't explained in the videos.

I thought nodes simply meant, no displacement. and anti-node meaning maximum displacement.
• Hi. When you blow over top of soda bottle a standing wave is set up. But why isn’t a travelling wave set up? In other words, what determines whether the wave will be travelling or standing? Many thanks for these fabulous videos!! Brian
• The wave that is created is in the bottle, where would this traveling wave travel?
• I was kind of confused on when he said left and right. Do the air molecules move horizontally based on they gravitational pull upon them or is there another way to tell why they move how they do?
• They move parallel to the direction in which the wave propagates.