Can someone explain to me, how does rotation work? I thought before that rotation of an object could be described by an axis through the mass center of the object, and an angular velocity (this would be equal to describing the rotation as an angular momentum). This means that the rotation would cause the object to turn around 360 degrees in a certain time, and come back to the same possition after a whole turn. But if I throw a pen up in the air, it wont be as simple as that. It will rotate fast around one axis (the one going through both ends of the pen), but it will also wobble. So after it has turned one time around the axis, it will not be back in the same possition, since it has also wobbled a little bit. So, how do you describe rotation, and how do you use it in calculations?