How do we know that something is moving you ask, well it has to do with comparing it to other objects. Motion is hard to detect if you have your eyes closed, because you cannot tell if something is moving by seeing go past something else. Think about a car that has whizzed past you. You could tell that they were moving (not too fast I hope ☺) by comparing the car’s movement your mailbox, driveway, your bike that is laying in the yard, or your friend’s house across the street.