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Settling is sediment that has settled at the bottom of a liquid. Also called sediment.

Settling velocity or fall velocity or terminal velocity (ws) of a (sediment) particle is the rate at which the sediment settles in still fluid. It is diagnostic of grain size, but is also sensitive to the shape (roundness and sphericity) and density of the grains as well as to the viscosity and density of the fluid. It integrates all of these into a key transport parameter.

Stoke's Law predicts the settling velocity of a small sphere in a fluid. The fluid may be air or water, and the law finds many applications in the natural sciences. Stoke's law is:

where w is the settling velocity, ρ is density (the subscripts p and f indicate particle and fluid respectively), g is the acceleration due to gravity, r is the radius of the particle and μ is the dynamic viscosity of the fluid.

Settleable solids are the particulates that settle out of a still fluid. Settleable solids can be quantified for a suspension using an Imhoff cone.

See also: Sedimentation

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