system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When a balloon pops, what is actually creating the sound I hear?
gpt
Expanding air.  

Sound is just vibrating molecules.  When you play music from speakers, the speakers vibrate the air and those vibrations get picked up by our ears.  Stronger vibrations sound louder, and smaller ones are quieter.

When a balloon pops, all of the air inside is suddenly free to expand.  So it does, instantly and with quite a bit of force since it was at a lot higher pressure than the outside air.  Our ears perceive this big pressure wave as a bang.