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Wineglass Normal Modes

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Added by Admin in Mechanics
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Description

The first two normal modes of oscillation for a wineglass subjected to amplified sound. The fundamental mode (529.3 Hz) and the second mode (1368.0 Hz) are observed with the help of a strip of paper and a strobe light.The fundamental mode has 4 antinodes. This is the dominant frequency of the glass and is the easier of the two to find. We usually break the glass in this mode.

The second mode has 6 antinodes. To find its frequency we used HairerSoft's Amadeus Pro to find the approximate range and then zeroed-in more closely using a microphone and oscilloscope. We used a much higher sound intensity level than for the fundamental to produce the amplitudes pictured here.

Ear and eye protection should be used when trying this at home.

During filming we did not intend to break the glass. No audio was recorded along with the footage of the glass under the strobe, so we had to steal the sound of it breaking from other footage--hence the sudden "OOMPH" noise at 2:16 in the soundtrack.

For more details on our setup and references for further reading, see http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyword=k16940&panel=icb.pagecontent263162%3Ar%241%3Fname%3Dindepth.html&pageid=icb.page80864&pageContentId=icb.pagecontent263162&state=maximize Special thanks to Nils and Rob for letting us use the lab space.

Tags: Mechanics

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