Settling is the process by which particulates settle to the bottom of a liquid and form a 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.

For dilute suspensions, Stokes' Law predicts the settling velocity of small spheres in fluid, either air or water. Stokes' Law finds many applications in the natural sciences, and is given by:

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.

Stokes' law applies when the Reynolds number is less than 0.1.

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

沉淀是微粒沉降到液体底部并形成沉淀物的过程。

一种(沉淀物)微粒的沉淀速率或者叫下降速率或未速是微粒在静止液体内的沉淀速率。它可以诊断微粒大小，但也敏感于微粒形状(圆度和球度)、密度以及液体的密度和粘度。它将所有这些综合为一个关键的 运移参数。

对于稀悬浮液，斯托克斯定律可预测小球在液体中、水中或空气中的沉降速率。斯托克斯定律在自然科学中有许多用途，它是这样表示的：

式中，W是沉淀速率；p是密度(下标p和f分别代表微粒和液体)；g是重力加速度；r是微粒半径；μ是液体的运动粘度。

雷诺数小于0.1时，斯托克斯定律适用。

沉淀性固体是从静止液体中沉淀出来的微粒。

悬浮液中的沉淀性固体可用双层沉淀池或锥形沉淀池定量测定。