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Question:
Why do wine glasses make a ringing sound when you move your finger around the rim? How dose the liquid in the glass effect the sound?



Replies:
Sliding your finger around the rim of a glass sets up vibrations in the glass. The dominant vibrations are determined by the shape and size of the glass. The addition of liquid changes both the size and shape of the glass. In general, it makes the resonating glass smaller, so the frequency tends to increase with increasing amounts of water. Be aware that all "glasses" are not created equal. In particular "crystal" rings better than common glass. There are several reasons for this. Some are: 1. Crystal is more carefully crafted so that the shape is more precise than common glass. Distortions in the shape tend to produce vibrational interferences, so that the sound is not so "clear". 2. Crystal tends to be thinner than glass. This also contributes to the "cleanness" of the vibrations. Also being thinner reduces dampening of the vibrations so the vibrations tend to last longer. There are other more subtle comparisons, but this gives you some idea.

Vince Calder



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