Hi, I´m doing a school project about the history of physics and I think I could use your help. When we study Newton´s laws in school there´s often no justification as to why they are the way they are. Particularly, the third law just seems Newton´s wild guess. There seem to be no good alternatives to it, since they lead to wrong predictions (if body 1 exerts a force on body 2 and body 2 doesn´t exert any force on body 1, then we could have the reverse if we started thinking first about body 2: then, body 1 would be the one that exerts no force - hope this isn´t confusing.) So, can you cook up any explanation on why action equals reaction? P.S.: I think the second law can be expected from the first, which in turn is well justified, if you think of a frictionless floor.