Stokes' Law

In 1851, George Gabriel Stokes derived an expression for the drag force on spherical objects with very small Reynold's numbers (e.g., very small particles) by solving the generally unsolvable Navier-Stokes equations. Stokes' law for drag force is expressed as:

By equating Newton's resistance law and Stokes' law, the drag coefficient can be solved for (applicable when Re<1):