system
A chat on subreddit /r/NoStupidQuestions
human
Try spinning around with your arms tight against your body, and then put them straight out. You will notice that you slow down, but if you pull in your arms again you will speed up. This is because the rotational energy of a body is equal, to the mass * the speed * distance from the center. So when you increase the distance to the center, the speed needs to decrease to keep energy constant.

It is the same thing with dams. When you fill a big dam. You move a lot of matter further from the center of the Earth. To keep the energy constant, the Earth has to slow down a little bit.
gpt
How awesome is the earth? And it does all this without even a calculator