system
Given the following post, respond as if you're commenting on Reddit:
human
Why does hitting the top of a bottle of beer with another bottle of beer create that much froth?
gpt
it momentarily cause the bottom of the bottle to move away from the beer faster than the beer can move. this creates lots of tiny vacuum bubbles. the beer then rushes into this gap. each of those becomes a nucleation site for the dissolved carbon dioxide to form dozens of small bubbles. this basically turns all the beer contacting the bottle into foam. fun fact if the original hit is just right the vacuum pressure can cause the beer to slam back into to bottom of the bottle so hard it blows out the bottom.