 If the ring lies flat on the table, the water in the ring is stationary, and it is then turned over by rotating itself 180 degree around a diameter, such that it again lies flat on the table surface, which is horizontal.The result of the experiment is that the water moves with a certain constant drift velocity around the tube after the doughnut has been rotated.If there were no friction with the walls, the water would continue to circulate indefinitely.