Can you recall what centrifugal force is, and think why a molecule with higher mass/density would sediment faster?
Centrifugal force or fictitious force is the force that appears to act on the object as seen in a rotating reference frame and directed away from the axis of rotation. It does not exists when measurements are made in an inertial frame of reference.
Higher mass means that there will be higher gravitational force acting on it. The momentum is the product of mass and velocity of the particles so this means mass and velocity are inversely proportional to each other as the momentum distribution is constant. This means in higher mass, velocity will be less in centrifuge process. so higher mass particles comes to rest soon than lighter particles.
As samples spin in a centrifuge the particles in each sample are subjected to centrifugal force. However, this force is proportional to the mass of the particle. To express the centrifugal force applied to a particular molecule its molecular weight (M) is used in the formula:Centrifugal force =