OK, the standard deal here: this is harder than it looks. (Sounds???)
Just for some fun with my son I have resurrected an old lecture demo from the back room that, as far as I can tell, has not been used for at least 20 years. I have the PA horn driver, the amplifier, the box with plastic double pane windows, oscillator, etc. If I scratch the glass with a triangular file I can get it to fail, but otherwise I have not been able to break the glass with sound only.
In searching the web it seems that there are lots of views and lore about this demo. Some people say to use Pyrex beakers, some say to use only fine crystal, etc. I tried using cheap Wal-Mart wine glasses (I'm sure that those are too thick).
We did try the trick of putting a straw in the glass to find the resonant frequency (works great). I think the problem is my choice of glass and my pocket book, I would really rather not break $40 crystal wine glasses if I can avoid it.
So, to those of you who do this demo: what glass do you use? What tricks have you found?
Thanks,
John
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John E. Sohl, Ph.D.
Professor of Physics
Weber State University
2508 University Circle
Ogden, UT 84408-2508