And sometime T afterwards, this is position two. Now, let's suppose this is the particle shown in blue that we are studying inside our homogeneous mixture. And so this is the particle that we basically want to discuss and we want to basically answer the following question what forces are acting on that particle? Well, first of all, because this test tube is being rotated in a circular motion, what that means is we know from physics this particle will have a certain tangential velocity. And the velocity here, the vector, will point tangent with respect to the circle. So this is why the velocity basically points this way for this particular particle.