 And so in other words, this is a very strong intuition that we have, that that is normal. And so all of this was so convincing and reasonable sounding that over the next thousand years it became accepted knowledge. People were taught it, educated people were taught it, would teach other people. It became Christian church dogma. And really over the next thousand years, the only things that happened is that various people worked on trying to improve the details of this idea of violent motion. So if you pick up a brick and you throw it, once you've given it that force, you can make it move and make it not be on the ground. But once you let go, why does it keep moving for a while? Why doesn't it just stop and be on the ground at the same time suddenly? And how do you get through the details of that? And people invented ideas of things called impetus, which is the set of ideas that try and describe from an Aristotleian point of view how something that's been thrown keeps moving even once you let go of it. And this was invented by a Greek philosopher and subsequently refined and analyzed by Persian philosophers and then eventually Western philosophers until finally it came to Galileo Galilei, who after a large number of careful experiments and measurements and a lot of thought came to the conclusion that the problem wasn't in an insufficiently detailed model of impetus but rather with Aristotle's fundamental idea of natural and violent motion. And instead Galileo said that rather than requiring a force to make something move, if you don't apply a force to something, then it will keep moving exactly the way it was moving. So if something was at rest, then with no force it will stay at rest. But if something is moving, then if you don't apply a force, then it will keep moving.