system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the sound of filling up a water bottle change the higher up it gets?
gpt
Because as the bottle fills the space the sound is bouncing around changes. When you're filling up an empty bottle the sound is coming from relatively far away, as opposed to the top where it's moving a small distance and thus has a different frequency (sound). It's similar to putting your finger on a closer to further hold on a wind instrument, but with water.