Proof Of Critical Speed Equation In Ball Mill. ensp0183enspThe critical rotational speed ratio 207 of the vessel, defined as the ratio of the operating speed n to the ideal critical speed nc 2.35 s 2261, i.e., 207 nnc, which was determined as nc 2gD 0.52207 g gravity acceleration, D vessel diameter from the equilibrium of gravity and centrifugal force acting on a ball.