Vibrations in a glass with water.

[Observeraren]

So I just poured water in a glass to clench my thirst. Hit the 2/3 empty glass with a pen and a high frequency started resonating for a brief moment, which I percepted as sound. When I tilted the glass the tilt resulted in change of frequency. When the glass was empty there was no change in frequency. The frequency did not change when the glass was rotated in such manner that the water did not change it's horizontal positioning or not atleast in a way that was observable by ear.
This left me thinking that the vertical movement of the water interfiered with the resonance of the glass, "damping" the vibrations at the direction of the tilt. But at the same time the horizontal tilt is releasing vertical space in the opposite direction of the tilt. So this does not make much sense, does it?

Then I'm left wondering how the series of vibrations are perpendicular to the glass or am I looking at this from a completely wrong angle? Or is the work done from the force behaving like a wave? I have a tiny tickle of this but I could be so wrong, afterall having nearly no education in physics.
I've just started dabbling in Fourier Series by Georgi P. Tolstov, starting with introduction to real analysis by A.N.Kolmogorov & S.V.Formin, which is way ahead of me considering that I have not yet finished the book on fundamental concepts of algebra which I find easily understandable.

TL;DR: A glass is filled with an unsubstantial amount of water. When I tilt the glass that as been struck with force. Why does the frequency of the resonation change.

EDIT: I did not take to my count that the water also forwards the force. But I'll leave this question to you for now.

Kind regards; Observeraren

 

[davenn]

to clench my thirst.

I think you meant quench

When the glass was empty there was no change in frequency

this doesn't sound correct as it goes against having glasses filled with different levels to produce different tones
note ... along with different water levels different sizes are also used

also a single glass with different levels
http://www.bing.com/videos/search?q...&mid=94FB2E76EACA8DE0C51794FB2E76EACA8DE0C517

When I tilted the glass the tilt resulted in change of frequency.

that would be expected as you are changing the shape of the resonant chamber

Dave

 

[DaveC426913]

I haven;t formulated an answer yet, but a good start would be to take into account the form of vibrations in a hollow cylinder.

This is a crude online image I found but it makes the point.

 

[DaveC426913]

I think you meant quench

Nono. He meant clench.

this doesn't sound correct as it goes against having glasses filled with different levels to produce different tones
note

I think you misinterpreted that. I believe he meant his empty glass did not change frequency when tilted versus untilted.

 

[davenn]

An empty glass does not change frequency when tilted versus untilted.

ahhh yes on that point agreed I probably misread

but the partly filled tilted and untilted will make a changeD

 

[Observeraren]

I think you meant quench

Yeah! That was definately the word I was after.

you are changing the shape of the resonant chamber

Well this sums up the change in frequency for me!

This is a crude online image I found but it makes the point.

From the right-hand drawing I interpret the crest of these vibrations to be perpendicular to the glass. Is this the case?

I think you misinterpreted that. I believe he meant his empty glass did not change frequency when tilted versus untilted.

Confirmed!

EDIT: It's 1:32AM over here. Thanks for the discussion so far! Good night!