# Wine glass sound physics behind

## Main Question or Discussion Point

when you slide your thinger around the rim of glass it produces resonance

the matter which vibrates is a glass, not air, right?

i understand that when ou hit a glass once it produces sound as by hitting you displace mass of glass from its equilibrium.

but why sliding the rim produces sound? if it is due to displacement caused by weight of the finger placed on the rim, then why sliding the wall of the glass does not produce sound?

thank you

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A.T.
when you slide your thinger around the rim of glass it produces resonance

the matter which vibrates is a glass, not air, right?
Both. If you can hear the sound the air vibrates. The glass vibrates as seen here:

but why sliding the rim produces sound?

if it is due to displacement caused by weight of the finger placed on the rim,
It is the friction between the surfaces.

then why sliding the wall of the glass does not produce sound?
It does. But putting the finger on the wall it might dampen the oscillation more than on the rim.

1 person
olivermsun
It is the friction between the surfaces.
An important feature of a lot of these musical "instruments" is actually a kind of stick-slip motion (typically aided by, e.g., a wetted finger) that needs to be "synchronized" with the natural resonance in the system.

A.T.
An important feature of a lot of these musical "instruments" is actually a kind of stick-slip motion (typically aided by, e.g., a wetted finger) that needs to be "synchronized" with the natural resonance in the system.
Yes, you need a regularly oscillating friction force, which happens when static and sliding friction alternate due to elastic interaction. And then you have to move the finger at the right speed to get the frequency right.

However, if it is a matter of friction, does this imply that rubbing one single spot on the rim will also produce resonance? or it is due to the fact that keeping the finger at one spot will damp produced by this spot oscillations the finger should move?

upd. i guess it is answered in the previous post, did not see it before posting

if oscillations produced by alternating static an moving friction, then as far as i know static friction occur until object is displaced, therefore in a moving finger case, alternation between static and moving friction should not occur as once finger is displaced there is only moving friction afterwards?

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A.T.
if oscillations produced by alternating static an moving friction, then as far as i know static friction occur until object is displaced, therefore in a moving finger case, alternation between static and moving friction should not occur as once finger is displaced there is only moving friction afterwards?
The finger is not a rigid body. The skin at the contact patch deforms.

olivermsun