This conglomeration changes the particle s shape, increases its size, and may affect the specific gravity. These increases allow the particle to settle more rapidly than a discrete particle. On a graph of settlement vs. time, the plot begins as roughly linear, then dips downward, indicating the increase in settling velocity corresponding to the increases in particle shape and size. Reynolds' Number vs. Coefficient of Drag As was mentioned in the derivation of Stokes Law, the coefficient of drag C D is related to the Reynolds number. The Reynolds number is a relationship between the velocity of a particle and the viscous forces acting upon it.
C D is related to the viscosity of the fluid through which the particle is traveling.
Since these two parameters are based on the same fluid property, a relationship can be derived between the two of them. We relate Stokes Law to spherical particles when we simplify the relationship between volume of the particle and area of the particle. The formula used in place of the volume of the particle, is the equation for the volume of a sphere. Using this equation in the derivation of Stokes Law builds the assumption of spherical particles into the equation. We can relate Stokes law to non-spherical particles by applying the shape factor, F , to the denominator of the equation.