Sedimentation:

The process of sedimentation has been used to measure the size of large molecules, where the force of gravity is augmented with the centrifugal force in a centrifuge. Sedimentation is the tendency for particles in suspension in solution to settle out of fluid in which they are entrained, and come to rest against the wall. This is because of their motion through the fluid in response to the forces acting on them: these forces can be because of gravity, centrifugal acceleration or electromagnetism. Sedimentation may pertain to objects of various sizes, varying from large rocks in the flowing water to suspensions of pollen and dust particles to cellular suspensions to solutions of single molecules such as  peptides and proteins . Even small molecules like aspirin can be sedimented, although it can be difficult to apply a strong force to produce significant sedimentation. Eutrophication is an increase in concentration of the chemical nutrients in an ecosystem to an extent that increases the primary productivity of ecosystem. Other species can experience an increase in population that negatively affects other species in the direct ecosystem.

In the sedimentation experiment, the applied force accelerates the particles to a terminal velocity vterm at which the applied force is canceled exactly by an opposing drag force. For small particles, the drag force varies linearly with the terminal velocity. Likewise, the applied force generally varies linearly with some coupling constant q, which depends only on the properties of the particle, F_app = qE_app. The concentration of particles at the boundary is certainly opposed by the diffusion of the particles. The sedimentation of particles under gravity can be described by the Mason-Weaver equation, which has a simple exact solution.

The sedimentation coefficient s in the case equals m_b/f, here m_b is the buoyant mass. Particles with a dipole moment can be sedimented by an electric field or electric field gradient, respectively. These processes are called as electrophoresis and dielectrophoresis. For electrophoresis, sedimentation coefficient corresponds to the particle charge divided by its drag. Likewise, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its drag.