I have created such a thread in the past but it was misinterpreted and I havent been given the help I needed , this time I shall explain more about what is going wrong through a figure . sorry for my bad english. topic: when a 3d body is going at constant velocity in a straight line and suddenly a force in its center of gravity was applied and has a certain angle with its initial velocity vecotr the body will make a turn and it will go in a curvilinear path if this force persist , my question why does that body when it turns it turns like in case "1" in the image below and not like in case 2 in the image: [URL]http://www.mypicx.com/uploadimg/913064521_04142010_1.jpg[/URL] and when does a body rotate like in case 2 ? if the same body shown in the figure has a propeller engine that when is activated its force acts on its center of gravity and perpendicular to it s initial velocity will the body rotate the same way as in case 1 or it shall go sideways like in case 2 ? please help telling me the difference .