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.
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