[Physics] Why the sound of filling water into a bottle rise in its frequency

Question

We have all observed the rising tone of water while it's getting poured into a container.Why,in the language of physics, does this happen?

Answer 1

The resonance cavity at the top gets smaller as you fill and that chamber is essentially what you hear when you fill. The smaller the resonance cavity, the shorter a single wave would fill it end-to-end and therefore that frequency goes up. As you fill, the sloshing noise that fits that frequency "echoes" (bounces a few times because of the size of the container), then leaves the top so you hear it. That process repeats until the bottle is full (and in the end, no resonance cavity).