system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do yo-yos work?

Saw someone playing with one today, just going up and down, and I've always wondered if it's because of the momentum of the body when it hits the end of the string.
gpt
Adding to the other answer. A good yo-yo won't have the string tied tight to the axle either. It will just be looped. So the yo-yo can be thrown down picking up the spin, then keep spinning at the bottom in the loose loop. When the player wants the yo-yo back, a little jerk on the string causes it to "snatch", creating enough friction for the string to start winding back onto the axle, bringing the yo-yo up to the hand. That's the basis of tricks like "walking the dog" where the yo-yo spins at the low point, then is touched on the ground so the spin makes it roll forward a little before being brought back up with a jerk on the string.