Date: Tue Mar 31 23:13:30 2009 Back to Contents ------------------------------------------------------------------------

Author: Paul Nord

Subject: Re: Ruben's tube and propane

Post:

Urs,

Check out a copy of Mac AudioToolbox:
http://www.blackcatsystems.com/software/audiotoolbox.html

Cute function generator. Nice little sweep generator. You may find
it informative for your development of the LabView tools. The
logarithmic sweep, for example, is a very practical feature for
demonstration.

I'm a little confused by your use of the terms "node" and "knot".
I've typically heard the terms "node" and "anti-node". Node is used
to describe places where there is little or no motion. Anti-node is
used to describe the places where there is a lot of motion. Or, in
the case of a pipe replace the word "motion" with "pressure change."

Do we all agree that the flames come out of the "anti-node" locations?

Paul

On Mar 31, 2009, at 3:46 PM, Urs Lauterburg wrote:

> Cliff,
>
> 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
>
> Urs Lauterburg
> Physics demonstrator
> Physikalisches Institut
> University of Bern
> Switzerland
>
>
>> 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.
>>
>> Cliff
>


From tap-l-owner@lists.ncsu.edu Tue Mar 31 23:13:30 2009

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