pure resonance occurs when the internal and external natural frequencies match.

The more water you add to the glass, the slower the glass vibrates, creating a lower pitch and adding water to the glass decreases the amount of air space, which means there is less air to vibrate. With less air, the vibrations happen more quickly and produce a higher pitch.

Sound in water and sound in air travel in similar ways. They are both waves that move similarly. The amplitude of a wave is related to the amount of energy it carries.

This sound is created when the vibrations of the glass affect the air inside the glass. Each glass vibrates at a characteristic pitch called the resonant frequency.

No because there is too much friction between the glass and your finger

the lowest frequency is of water is 22.235 GHz (gigahertz)
glass is resonance frequency is between 20-20,000 Hz (hertz)

The amplitude of a sound wave is a reflection of how much energy is carried, which contributes to the intensity of the sound. Intensity is measured in decibels and is perceived as sound volume. Thus, the volume is proportional to the amplitude of the sound wave. The frequency of a sound wave is perceived as pitch.

Amplitude, Compression, Rarefaction, Ambient pressure

f= 1/2pi X Square root (L x C)
f= frequency in hertz
L= inductance in henrys
C= capacitance in farads

The more water in a cup the lower the pitch. The volume of water in the glass is making the glass heavier and therefore its more difficult for the glass walls to vibrate