Notice:  As of December 14, 2016, the MindBites Website and Service will cease its operations.  Further information can be found here.  

Hi! We show you're using Internet Explorer 6. Unfortunately, IE6 is an older browser and everything at MindBites may not work for you. We recommend upgrading (for free) to the latest version of Internet Explorer from Microsoft or Firefox from Mozilla.
Click here to read more about IE6 and why it makes sense to upgrade.

Physics In Action: Sound Waves in a Flaming Pipe


Like what you see? Add it to your library to watch it online or download.

You Might Also Like

About this Lesson

  • Type: Video Tutorial
  • Length: 6:01
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 64 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Physics (147 lessons, $198.00)
Physics: Waves (19 lessons, $27.72)
Physics: Sound (5 lessons, $5.94)

This lesson was selected from a broader, comprehensive course, Physics I. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers kinematics, dynamics, energy, momentum, the physics of extended objects, gravity, fluids, relativity, oscillatory motion, waves, and more. The course features two renowned professors: Steven Pollock, an associate professor of Physics at he University of Colorado at Boulder and Ephraim Fischbach, a professor of physics at Purdue University.

Steven Pollock earned a Bachelor of Science in physics from the Massachusetts Institute of Technology and a Ph.D. from Stanford University. Prof. Pollock wears two research hats: he studies theoretical nuclear physics, and does physics education research. Currently, his research activities focus on questions of replication and sustainability of reformed teaching techniques in (very) large introductory courses. He received an Alfred P. Sloan Research Fellowship in 1994 and a Boulder Faculty Assembly (CU campus-wide) Teaching Excellence Award in 1998. He is the author of two Teaching Company video courses: “Particle Physics for Non-Physicists: a Tour of the Microcosmos” and “The Great Ideas of Classical Physics”. Prof. Pollock regularly gives public presentations in which he brings physics alive at conferences, seminars, colloquia, and for community audiences.

Ephraim Fischbach earned a B.A. in physics from Columbia University and a Ph.D. from the University of Pennsylvania. In Thinkwell Physics I, he delivers the "Physics in Action" video lectures and demonstrates numerous laboratory techniques and real-world applications. As part of his mission to encourage an interest in physics wherever he goes, Prof. Fischbach coordinates Physics on the Road, an Outreach/Funfest program. He is the author or coauthor of more than 180 publications including a recent book, “The Search for Non-Newtonian Gravity”, and was made a Fellow of the American Physical Society in 2001. He also serves as a referee for a number of journals including “Physical Review” and “Physical Review Letters”.

About this Author

2174 lessons

Founded in 1997, Thinkwell has succeeded in creating "next-generation" textbooks that help students learn and teachers teach. Capitalizing on the power of new technology, Thinkwell products prepare students more effectively for their coursework than any printed textbook can. Thinkwell has assembled a group of talented industry professionals who have shaped the company into the leading provider of technology-based textbooks. For more information about Thinkwell, please visit or visit Thinkwell's Video Lesson Store at

Thinkwell lessons feature a star-studded cast of outstanding university professors: Edward Burger (Pre-Algebra through...


Recent Reviews

This lesson has not been reviewed.
Please purchase the lesson to review.
This lesson has not been reviewed.
Please purchase the lesson to review.

We know that sound is a wave phenomenon. Specifically, it's a pressure wave in air, for example. And as with other wave phenomena, we expect to be able to set up standing waves in appropriate situations. Remember for a string we could set up a standing wave where the string vibrates up and down, and the standing waves are standing waves because there are regions, which don't move at all. Those are nodes. There are regions, which move a lot, which are antinodes. We expect to see wavelike patterns set up in a column of air vibrating. We expect also to see regions of changing pressure; high and low pressure, and we can demonstrate that with this apparatus over here.
Now this apparatus consists of a long pipe into which we've drilled a whole bunch of holes along here, which you'll see shortly. And what we're going to do is introduce into this pipe some gas with this tube over here, and we're going to light up this pipe so you can see a whole bunch of flames standing on the pipe. Let's see how that looks. Okay, we have our pipe; gas being introduced; and the flames now are our way of telling something about the pressure inside this pipe. Now, what is of interest to us is what happens when we push the air in this pipe with some signal generator, something that's going to compress and rarefy the air, push it in and out. And that's going to be achieved by this loudspeaker, which is attached to one end of this pipe. This loudspeaker in turn is connected to a signal generator. So let's see what's going to happen.
When you turn on the signal generator, it's going to send a signal, a tone line hmmm down this pipe. The signal is going to bounce off and do whatever it wants to do, and we expect to see some standing wave pattern, which would be analogous to the standing wave pattern we saw in a vibrating string. What you expect to see is a wavelike behavior, and that's what we want to demonstrate now. You'll see that there are regions where the wave is high, regions where the wave is low, and that wavelike pattern shows us that sound, which is what is producing the wavelike pattern, is obviously a wave, which is the point of this demonstration.
Okay, so I'm going to turn on the signal generator now, and now let's see what we see. Let's take a look at the pattern. You see that there are regions where the flame is high and also somewhat yellow, and regions where the flame is low and somewhat blue. Now what's interesting is that I can change the position of the regions where the flame is high and the regions where the flame is low by changing the frequency, which is what I'm doing. I change it one way, change it another way, and let's just watch this for a few seconds and see what happens. Now visually you clearly see a visual representation of the wavelike nature of sound on this tube, the picture being transmitted to us by means of the flame, which obviously has a wavelike behavior.
We've seen that a simple tone produces simple wavelike pattern of the gas flames on this tube. Now let's see what happens if we look at a real piece of music. You see that with a real piece of music the flames jump around. As you can hear, when the music gets louder, the flames jump higher. When the music gets lower, the flames are lower. You can also see that this pattern is more complicated because a real piece of music has a more complicated mixture of different frequencies, different notes that you hear. Let's watch the music for a few seconds. Notice at various points the sound really gets loud and the flame gets higher. If we turned up the sound even more, we'd actually blow out a bunch of the flames. That reflects the fact that increasing amplitude of sound represents an increasing pressure inside the tube, and at the appropriate point the flames can get very, very high and you could see some of the flame actually going out. Notice that's happening right now.
Again, the point in this demonstration is, one, to notice the connection between the amplitude of the sound, the loudness, and the amplitude of the flames shooting up. The flame is now measuring the pressure change caused by the loud sound. And again you note that we don't get a simple pattern of evenly spaced high flames and low flames. What we get now is a more complicated pattern reflecting the more complicated nature of a real piece of music.
So now let's summarize what we've learned. We know that sound is a pressure wave, and one way of showing this is to make that pressure wave visible by means of this apparatus over here. The flames tracked the different pressures that this tube carried. There are regions where the pressure is higher; there are regions where the pressure is lower. And those regions of high and low pressure are spaced as high pressure, low pressure, high pressure, low pressure, and so on, and form a regular wave pattern. For a simple frequency, the drive in the air and the gas in the tube, we see a simple regular patter reflecting the fact that sound is, after all, a pressure wave. For a more complicated piece of music, we see a more complicated pattern but the message is still the same. Sound is a pressure wave, and those changes in pressure reflect themselves in the changes in the heights of these flames.
Physics In Action: Sound Waves in a Flaming Pipe Page [1 of 1]

Embed this video on your site

Copy and paste the following snippet: