What is the physics behind the different frequencies of glasses of water?

mai: What is the physics behind the different frequencies of glasses of water?
We are studying sound waves in physics now. I was wondering if anyone knew anything about the physics behind how sound waves work when you tap a glass of water. Why do the water levels dictate the pitch of the sound?

Answers and Views:

Answer by Ossi G
Hello

The more water you fill in, the shorter is the air column in the glass. One would expect, that this would result in a higher tone.

But different to what one would expect, the pitch of the sound gets the LOWER, the more water you fill in.

The reason seems to be that with more water more mass must be moved by the oscillating glass walls. Which makes the oscillation slower, and the pitch of the sound lower.

More to this is written here:
https://www.drphysics.com/teacup/teacup.html

Regards