“After I had finished a tuning fork oscillator, my brother challenged me to make an oscillator using a wineglass. ( https://www.instructables.com/id/Tuning-Fork-Osci… )
He thought it would be more difficult to use a wineglass than a tuning fork as the frequency determining element. It is.
Everyone knows the sound a (wine) glass makes when you gently tap it, usually it sounds like a fast decaying “ping”. Some, more expensive glasses can keep “singing” when you rub a wet finger over the edge. The sound this produces is caused by the glass quickly vibrating in a special way. The round shape of the glass changes into an ellips, back into a circle and then into an ellips but rotated by 90 degrees, and so on. The air vibrates with the glass and a tone is the result.
You can even find serious research on the vibrations of wineglasses, just Google for : “a study of wineglass acoustics” and see the pdf below. (I admit I didn’t read it all)”