2. Aerosol sedimentation

In this paragraph, we study the movement of particles under the action of gravity.

In aerosol physics, fall velocities and translational velocities of electrically charged particles subjected to the action of an electric field are often used, leading to limit velocities. In fact, these limiting velocities result from a balance between two forces, one of which may be the action of the Earth's gravitational field on the particle, or the electric force acting on it, the other being none other than the resistance of the support medium, which, in general, is accessible to theory, as we shall see.

Only, the dimensions of aerosols vary in the ratio of 1 to 10 ⁶ , so that the same support medium can, depending on the case, be considered as a continuous fluid or else as a discontinuous corpuscular medium...