Look here: say you have

Look here: say you have a disk that can spin, and so you put a pail of milk on it and you make it spin. You will see the milk go up the side of the pail, and fly over and out onto the disk. No big deal, eh? The spin will make a pull. But now what if you said that the pail of milk is your "at rest"? Then you have you and the sky and all that in a big huge spin, and the disk with its pail of milk is the only body that is "at rest", yes? How can you say then why the milk goes up? What can make the at-rest milk fly out of the pail like that?