system
Given the following post, respond as if you're commenting on Reddit:
human
When rubbing a wine glass with a finger to produce a tone, why does the finger have to be wet?

You probably all know the story: I get bored, there's a wine glass on the table, I start to play with it, exploiting one of its resonance frequencies by rubbing it in a certain way with the finger. I know why that tone comes about and what influences its frequency.

But what I don't know is: why does it require a wet finger? Can one of you guys help me out?
gpt
Seems to me it's just because you want to lower the coefficient of static friction.

When your finger is dry and you're just about to break static friction and start sliding across, you're forcing with some very large shear. You break static and then you're finger jumps pretty far and you get stuck again. So the forcing looks like delta functions spaced by too long a period.

And as we all know, we want to force close to the resonant frequency. So wet your finger lower the coefficient and it will be much easier to break in to sliding at it will happen more often.

More importantly I've heard that the glass has to be crystal.