system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How was the speed of sound initially measured?
gpt
A clever trick is to beat a drum exactly once a second, then walk away, looking back. As you recede, the sound will get more and more behind the sight of the drum being beaten, until eventually it's in synch with the *next* beat. Then you know you're exactly one sound-second away. Do this in several directions to average out errors, and you have the speed of sound.

Doing this with a group of 11 year olds we got to within 5% of the correct value.