Date: Tue Mar 31 16:57:41 2009 Back to Contents ------------------------------------------------------------------------

Author: Urs Lauterburg

Subject: Re: Ruben's tube and propane



Actually I have just this morning demoed the Rubens tube (the Ziggy
version) and am about to consider myself kind of a Rubens tube expert
by now. I completely lost the fear of the burning gas filled tube by
now and am feeling that I have everything under control. Actually
it's all about adjusting it right, the proper frequencies, the
amplitude of the inputted sine waves and the amount of gas that you
let flow in. As I stated before, I generate very precise frequencies
with LabVIEW 8.6 on my little private MacBook Pro and that takes care
of the frequencies. However, I do adjust the amplitudes of the audio
amplifier and the rate of gas flow with a valve manually and have
gained as much practice to get very awesome standing waves from 5 to
13 nodes. At the end I have LabVIEW on the Mac play a little
composition with these tones.

I am planning to enhance the program to actually sweep the frequency
up between the nodes to demonstrate that not much happens if you
don't get the ''geometry'' right.

Now to your observation: I experienced the very same. If I turn off
the gas and if I leave the sound on I would get flames for a much
longer time, up to a minute or so, but if I turn the sound off, the
flames disappear immediately. My explanation is that without sound
there are no more pressure variations that push the gas out through
the holes.

I also noticed that I actually get a node at the far closed end where
I always thought that a closed pipe should show a knot there. On the
other hand it seems more plausible because pressure variations are
needed to get reflections for a standing wave. The speaker side on
the other hand, kind of shows something between a node and a knot
which kind of makes sense too because it's sort of a vibrating closed
end. The reflection mechanisms of longitudinal acoustic waves in
pipes are still kind of mysterious to me. Maybe I should consult Dick
Berg's book on sound physics again. I think he explains all that and
much more.

Best wishes from over here


Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern

>Thanks to everyone who responded. We went over the show this morning
>and the Ruben's tube worked fine on propane.
>I did notice one little odd thing: I had the sound on and we were
>finished so I turned the gas off at the stopcock on the tube. The
>flames continued to burn which didn't surprise me too much as I
>presumed the tube was still pressurized, but I reached over right
>away to turn the oscillator off and the instant I did, the flames
>went out. Was it just a coincidence? I'll see if I can reproduce it
>the next chance I get.
>The lecturer is going to show the Ruben's tube, double pendula (the
>nice ones I got last year) microwave single slit, laser single slit,
>quantum dots (the Cenco apparatus I asked about earlier), a humble
>simple pendulum and a couple of other things that I don't remember
>at the moment.

From Tue Mar 31 16:57:41 2009