So we define it by using an equation, the following equation. So, the sedimentation coefficient of a particle inside a test tube that is rotating with some angular velocity is equal to m, the mass of that particle multiplied by one minus V bar multiplied by Rho, where V bar is the partial specific volume. It's the reciprocal of the density of that particle. And row is the density of that medium, the fluid in which that particle is moving inside our test tube. And we divide the product by F, the frictional coefficient of that particle with respect to the fluid in which that particle is in. So, the question that we want to ask ourselves in this lecture is where exactly does this equation actually come from?