I have a physics test coming up in a couple of days and I really need to have some things explained to me. It is about something that I think is called in english "the velocity of the center of gravity" or something a long those lines. I have not been able to find anything anywhere about this so that is why I am here. In my physics book they roughly show the following: Sorry if the picture is somewhat unclear/poor resolution, but this is the best i could do when remaking it in paint. After having showed this derivation they mention something about the constant velocity of the center of gravity and stuff. To be honest i don't quite understand what they are doing here, what this means or what implications/uses you can have from this. Since my book does a poor job of explaining this, could anyone tell me what is going on in this picture, what this whole constant velocity of the center of gravity is and what uses you have from this/what it means. Illustrations with pictures, not too complicated answers and not too complicated physics language would be very much appreciated since I am only 18 years old. Any cool but not too complicated ways to calculate things with this would also be awesome if someone wants to provide it. I apologize beforehand for the language in this text, as english is not my first language. Would be happy to get answers asap!
The laws of motion apply to point particles, or to extended rigid bodies at the center of mass. Just as a particle without a (net) force acting on it will move with constant velocity, so does an extended rigid body without a (net) force will have its center of mass move with constant velocity.