What does pitch have to do with this?

Pitch is determined by the amount of water in the cup. The more water, the lower the tone. We can understand it this way: when knocking on cups, all cups are the same, so the factor of cups can be ignored. The difference is that the height of water is different, so the pitch depends on the level of water. The higher the water level, the shorter the air column, the faster the air column vibrates, the greater the vibration frequency and the higher the tone.

Characteristics of sound

Tone, loudness and timbre are three characteristics of sound; Tone refers to the sound level, which is determined by the vibration frequency; Loudness refers to the strength or size of sound, which is related to amplitude and distance; Timbre is a characteristic determined by the vocal body itself. Tone indicates sound level, which is determined by vibration frequency; Loudness indicates the size of sound, which is related to amplitude and distance; Timbre represents the characteristics of sound, and different vocal bodies have different materials and structures, so timbre is an important basis for distinguishing different vocal bodies.