Why does the pitch rise with the water?

Question

I just filled a plastic juice bottle, and noticed that the sound of the water filling the bottle rose in pitch as the bottle filled up. Before, I just took it for granted that the pitch rose as liquid filled something, but now I'm wondering why.

I'm a singer and lyricist, but not a physicist.

Answer 1

It's like a swanee whistle - as the bottle fills with water the vibrating column of air above it gets shorter and the pitch goes up

Answer 2

An open bottle acts like an open pipe. The standing sound waves generated are of a particular form with a "node" at the closed end (i.e. the level of the water) and an "antinode" at the open end. This boils down to the wavelength of the main note being four times the distance from the water to the mouth of the bottle. As the bottle is filled, this distance decreases and therefore so does the wavelength; the frequency is the speed of sound divided by the wavelength, so it rises and therefore the pitch of the note goes up.

Answer 3

An empty jar or glass will vibrate up the whole height with longer wavelength.
As the glass fills the shorter length of glass vibrates at a higher frequency.
A wire, string or elastic band acts the same way!

Answer 4

This happens for the same reason pitch goes up when a slide trombone slides inward, or when a guitar player shortens the strings with fingers pushing on them, or when a singer raises his or her voice box in the neck. It happens because smaller things have vibrate vaster which makes for a smaller wavelength of sound. Smaller wavelengths are heard as higher pitches.

Think about it this way, if you shorten the chain on a swing, doesn't it's frequency of swings go up? It's the same thing.

Answer 5

you are changing the length of the sound wave. not 100% sure haven't been in physics class in a long, long time.