What Are the Limitations of Stoke's Law?
The limitations of Stoke's Law are that it only applies when the viscosity of the fluid a particle is sinking in is the predominant limitation on acceleration. This means that the particle must be relatively small and slow, so it does not cause turbulence. Its accuracy in prediction also goes down if the particle is not spherical, the fluid is compressible, the motion is constant and no other particles interfere.
Stoke's Law uses known properties of a particle and a fluid to determine the velocity of a particle when its propelling force is exactly matched by the resistance of the fluid's viscosity. The most frequent force used is gravity, although it could be anything. When the conditions for the validity of Stoke's Law are not met, such as when the particle is very large or fast moving, so that the flow of the fluid around the particle is turbulent rather than smooth, Newton's Resistance Law applies instead.
Newton's Resistance Law does not address the viscosity of the fluid. Instead, it predicts the drag force resisting a particle's movement through a fluid where inertial forces dominate. This means that the tendency of objects to maintain their states of motion overpowers any inherent resistance of the fluid to flow.