I am currently working on my masters and happened to stumble upon screw theory, of which I have no previous experience with. Fundemental to screw theory is Chasles' theorem or Mozzi's theorem that states that any rigid body motion can be produced by a translation along a line and rotation about the same line, and vice versa. However, I find this hard to believe. Consider a body falling towards the ground while also rotating about an axis parallel to the ground and passing through the objects center of mass. How is it possible to represent this motion in screw-terms?