Also, the test tube confines motion to the direction down the length of the tube, so v B is opposite to u 1 and the Coriolis force is opposite to u 2, that is, against the wall of the tube. If the tube is spun for a long enough time, the velocity v B drops to zero as the matter comes to an equilibrium distribution. For more details, see the articles on sedimentation and the Lamm equation.