In this particular case, because we're undergoing angular motion, our acceleration is omega squared multiplied by R. Now, what is FB? What is the Boin Force? Well, once again, from classical physics, we know that the boine force is equal to not the mass of that particle, but the mass of the fluid that is displaced by that particle. So it's the mass of the fluid that is displaced by that particle. So we're going to designate that as M. This where this is displaced and it's multiplied by the acceleration, which is once again omega squared multiplied by R. Now, what is the force? Frictional.