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Old Sep 30th 2018, 09:09 PM   #1
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Question(s) about ‘singing wine glass’ experiment

Everyone knows that wine glasses with progressively more liquid in them will emit a higher toned sound when a damp finger is rubbed along its rim. It’s my understanding that tone/pitch is somewhat difficult to categorize scientifically, as frequency alone doesn’t tell the whole story. I would like to understand what physical, acoustical properties we would expect to change as more water is added to the glass.

To simplify our thought-experiment, let’s say the interior of the wine glass is a perfect cylinder. Would the resonance frequency of the glass change (increase) as the water increases? If the resonance frequency stays the same, what accounts for the increase in pitch? Would the amplitude of the sound wave increase with decreasing water in the glass? This seems to make sense to me since the walls of the glass would be able to vibrate more freely with lower levels of water. What about duration of vibration? Picture a vibration sensor affixed to the glass that stops firing once the vibration drops below a certain threshold. Would the time between striking the glass and the cessation of sensor firing be inversely proportional to the amount of water in the glass? And finally, since we assumed the glass was a perfect cylinder, would the relationship between these parameters be linear? Would it then be possible to calculate the amount of water in the glass from these parameters alone?

Thank you very much for reading my long lost. Any insight is appreciated!


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Old Oct 3rd 2018, 01:15 PM   #2
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Originally Posted by Stubby5000 View Post
Everyone knows that wine glasses with progressively more liquid in them will emit a higher toned sound when a damp finger is rubbed along its rim.
In reality the resonance frequency of the glass is lower when the glass is filled with water. You can hear and measure the pitch lowering.

Originally Posted by Stubby5000 View Post
It’s my understanding that tone/pitch is somewhat difficult to categorize scientifically, as frequency alone doesn’t tell the whole story.
The resonance frequency is the best parameter to investigate. It is easy to measure, highly reproducible, and in harmony with the model.

If you are interested in other parameters you might like a recent study by Lee. He measured the intensity of the vibration and concluded that the intensity is reduced when when the glass is filled. (link)

Originally Posted by Stubby5000 View Post
To simplify our thought-experiment, let’s say the interior of the wine glass is a perfect cylinder. Would the resonance frequency of the glass change (increase) as the water increases?
A perfect cylinder has no bottom and no rim. Increasing the water level in a bottomless cylinder has no effect.
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