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Ouch. That was painful to read.Nothing in the original note specified the stiction-excited oscillation was longitudinal.
Yes, it's very unlikely that the resonant frequency of a metal tube would match the resonant frequency of the air column inside. The wavelength would be the same. A hollow tube MIGHT couple the resonance of the tube to the air better than a solid tube.
My other issue with this statement is the term "big". It's not a very useful scientific term. This is like my daughter's 4th grade textbook which had this review question: "It takes a lot of ___ to stop an airplane." Given the choices the authors clearly wanted "force" which is not even true since a plane could be stopped with a small force (though perhaps over a distance much greater than the runway). 4th grade is probably too early to introduce impulse. I'll stop ranting here and leave the words "always" and "loud" alone.
Paul
On Sep 6, 2011, at 1:10 PM, Bernard Cleyet wrote:
"Another common physics demonstration that serves as an excellent model of resonance is the famous "singing rod" demonstration. A long hollow aluminum rod is held at its center. Being a trained musician, teacher reaches in a rosin bag to prepare for the event. Then with great enthusiasm, he/she slowly slides her hand across the length of the aluminum rod, causing it to sound out with a loud sound. This is an example of resonance. As the hand slides across the surface of the aluminum rod, slip-stick frictionbetween the hand and the rod produces vibrations of the aluminum. The vibrations of the aluminum force the air column inside of the rod to vibrate at its natural frequency. The match between the vibrations of the air column and one of the natural frequencies of the singing rod causes resonance. The result of resonance is always a big vibration - that is, a loud sound."