system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does water in a kettle go quieter just as it's about to boil?
gpt
The noise is caused by bubbles of steam forming at the bottom of the water and rising to the surface, but because they're moving through cooler water they condense and pop before they reach it, making noise as the water collapses into the space (this is a process called "cavitation"). When the kettle is about to boil properly all of the water in it is at or near boiling point, so a lot more of the bubbles make it through to the surface to get released as steam rather than popping inside the water.