What forces act on a solute particle in a gravitational field?

Three forces act on a solute particle suspended in a solvent and subjected to a gravitational field.

Frictional force (F_f)

As particles travel through a solution they experience a frictional drag proportional to velocity. When particle density exceeds that of the solvent, particles begin to sediment; as they begin to move along a radial path toward the cell bottom, velocity increases as radial distance increases.

Buoyant force (F_b)

Equal to the weight of fluid/solvent displaced.

Sedimenting or gravitational force (F_s)

The force introduced by centrifugation. It’s proportional to the particle mass and acceleration.