Stokes' Law Calculator
Drag force on a sphere in creeping flow (Re ≪ 1).
Instructions
1
Enter μ, r, v
Use SI units (Pa·s, m, m/s).
2
Ensure creeping flow
Valid for Re ≪ 1. For larger Re, drag deviates from Stokes' law.
3
Compute Fd
Click Calculate to get the drag force.
Formula
Fd = 6 π μ r v
Where: μ dynamic viscosity, r sphere radius, v relative speed.
Example: μ=0.001, r=1 mm, v=0.1 m/s ⇒ Fd≈ 1.885e−3 N.
Common Questions
Does density matter?
Density enters via Reynolds number validity. Stokes' law formula itself uses μ, r, and v.
Settling velocity?
Set Fd equal to net weight to estimate terminal settling speed of small spheres.