system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - Grandfather clocks, what keeps the pendulum and weight from losing momentum?

I've been looking into how they work over the past few days and I just can't wrap my head around why the weight and pendulum don't slow down. They seem to go against how I understand the laws of physics.
gpt
The weight is slowly pulled down by gravity, through a mechanism that gives the pendulum a tiny push on each swing to keep it going. Once a day or so, the weight needs to be lifted up to the top again, or else the clock stops when the weight hits the bottom and stops boosting the pendulum. So it's actually human muscle powering the clock, we just use the raised weight to store this energy (as gravitational potential energy) and slowly release it to power the clock.