

:: Section 3Newton's Resistance Law and Stokes's Law
II. Stokes's LawWhen small particle size and low velocity are involved, the Reynolds number is small and the flow is laminar. Under this condition, inertial forces are negligible compared to viscous forces. Newton's Law is no longer valid and Stokes's Law shall be used, which has the following form: In order to determine the drag coefficient in the Stokes's regime, we can compare the above equation to the Newton's resistance equation:
Then, we can get the drag coefficient in the laminar flow regime. It is inversely proportional to the drag coefficient Re_{p} as: There are several assumption associated with the Stokes's Law:
We should keep these assumptions in mind and verify if the assumptions are valid when we use the equation.
To calculate the Re_{p} values, you can use the webcalculator below: 