Date: Fri, 28 Oct 2005 13:06:06 -0400

Author: Gerald Zani

Subject: Re: Beaker Breaking Demo Question

Post:

Mike,

You might try using a small, fine file to score a little notch on the rim?
This may force a node at that point? The node might get the two closely
matched modes to spread apart from each other? Just a thought.

I use pyrex beakers. They're great, and best of all I can walk over to the
chemistry stockroom any time and take them off the shelf and charge it to
my account. -- JZ

At 11:59 AM 10/28/2005, you wrote:
>We do the same procedure of re-adjusting the frequency at a mid-range volume
>before cranking it up.
>Here's my latest problem:
>In the last end-of-year spending crisis I bought a bunch of wine glasses
>online. They all have two closely matched resonances (within about a Hz or
>so) and there is only about a 70% breakage success rate. They look nice on
>the screen, when the volume is cranked up the energy bounces around between
>modes and is fascinating to watch. Sometimes I can rotate the glass a bit
>and get it to break but I think I will have to bite the bullet and get a new
>batch. Anyone need 5 boxes of wine glasses?
>
>Mike
>
>On Thursday 27 October 2005 12:55 pm, Gerald Zani wrote:
> > Wolf,
> >
> > That's the best way to say.
> >
> > Is anyone else aware of the non-linear effect in the beaker breaking demo?
> > -- JZ
> >
> > At 11:47 AM 10/27/2005, you wrote:
> > >At any particular volume setting (or amplitude of glass vibration) you can
> > >always tweak the frequency a bit to maximize the motion of the
> > >glass. -- Wolfgang
> > >
> > >On Oct 27, 2005, at 10:52 AM, Keith Warren wrote:
> > >>OK, so when I do this demo, I tune it so they can see the glass moving
> > >>under a strobe light. Then I jack up the amplitude of the speaker to
> > >>shatter the glass. Granted, it is not always 100% successful. Are you
> > >>suggesting to actually increase the speaker frequency slightly before
> > >>turning up the volume? If so, any ideas how much.
> > >>
> > >>-Keith
> > >>
> > >>On Oct 27, 2005, at 9:40 AM, Gerald Zani wrote:
> > >>>Doug,
> > >>>
> > >>>Contrary to common thinking the resonance peak in this demo is not
> > >>>constant. It is a non-linear effect where the frequency depends on the
> > >>>amplitude. The resonance peak shifts higher as you increase the
> > >>> amplitude.
> > >>>
> > >>>This non-linear effect can cause tuning problems. There can be trouble
> > >>>breaking the beaker because when this is not accounted for. The beaker
> > >>>can be made to break more easily and with less power if you carefully
> > >>>tune it to compensate for the frequency shift as you increase the
> > >>> amplitude.
> > >>>
> > >>>You unknowingly shifted the frequency to the resonance peak when you
> > >>>increased the amplitude to break the beaker.
> > >>>
> > >>>
> > >>>Nothing like sipping hot apple cider and admiring the pumpkins under the
> > >>>blazing red sugar maples.
> > >>>-- JZ
> > >>>
> > >>>At 06:19 PM 10/26/2005, you wrote:
> > >>>>The other day, I was setting up our Beaker Breaking Demo and ran across
> > >>>>something I never noticed before. Using a microphone, when I looked
> > >>>> for peak resonance(or volume) on the oscilloscope, I got one frequency
> > >>>> like 1263.4 Hertz and when I tweaked it up bit, I got almost total
> > >>>> sound cancellation on the microphone (outside the sound chamber it was
> > >>>> still very loud) at 1264.2 Hertz. At both high and low settings I
> > >>>> have broken beakers. The microphone is positioned 90 degrees instead
> > >>>> of the 180 degrees (or opposite side) to the beaker and horn driver.
> > >>>>
> > >>>>Any idea why these two frequencies work? ...Doug J.
> > >>>
> > >>>Gerald Zani e-mail:
> > >>>Gerald_Zani@brown.edu
> > >>>Manager of Demonstrations phone: (401) 863-3964
> > >>>Department of Physics FAX: (401) 863-2024
> > >>>Brown University Providence, RI 02912-1843 USA
> > >>>
> > >>>http://www.physics
> > >>>.brown.edu/physics/demopages/demo/
> > >>> http://www.physics.brown.edu/physics/userpages/staff/Gerald_Zani/index.
> > >>>html
> > >>>
> > >>>Do a little more of that work which you have confessed to be good,
> > >>>Which you feel that society and your most Just Judge rightly demand of
> > >>> you. Cultivate the tree which you have found to bear fruit in your
> > >>> soil. If you have any experiments you would like to try, try them.
> > >>>Now's your chance.
> > >>>
> > >>>Henry David Thoreau, Journal entry, 1850.
> > >>
> > >>_______________________________________
> > >>
> > >>Keith Warren
> > >>Operations Manager
> > >>The Science House
> > >>keith_warren@ncsu.edu
> > >>www.science-house.org
> > >>(919) 515-5568
> > >>
> > >>Campus Box 8211
> > >>North Carolina State University
> > >>Raleigh, NC 27695-8211
>
>--
>Mike Timmins
>University of Virginia
>Acadamic Support Supervisor
>
>email: mat3q@virginia.edu
>phone: (434) 924-6800
>mail address:
>382 McCormick Rd
>Charlottesville, VA 22904

Gerald Zani e-mail: Gerald_Zani@brown.edu
Manager of Demonstrations phone: (401) 863-3964
Department of Physics FAX: (401) 863-2024
Brown University Providence, RI 02912-1843 USA

http://www.physics.brown.edu/physics/demopages/demo/
http://www.physics.brown.edu/physics/userpages/staff/Gerald_Zani/index.html

Do a little more of that work which you have confessed to be good,
Which you feel that society and your most Just Judge rightly demand of you.
Cultivate the tree which you have found to bear fruit in your soil.
If you have any experiments you would like to try, try them.
Now's your chance.

Henry David Thoreau, Journal entry, 1850.


From dimarco@physics.montana.edu Fri Oct 28 13:12:15 2005

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