Drag force on a sphere in creeping flow (Re < 1). Optionally compute Reynolds number and terminal settling velocity from particle and fluid densities.
Fluid Mechanics II1 cP = 1 mPa·s = 0.001 Pa·s
Optional — fluid and particle densities for Re check and terminal velocity
Stokes drag force (creeping flow):
Equivalent to FD = CD × ½ρV² × A with CD = 24/Re.
Terminal settling velocity:
Obtained by balancing drag, buoyancy, and gravity. Only valid when Re < 1 (verify after computing Vt).
Validity condition:
For Re between 1 and 1 000, use intermediate drag correlations (e.g. Schiller-Naumann). For Re > 1 000, use the drag-sphere calculator with CD ≈ 0.47.
Where:
Common particle densities:
| Material | ρ (kg/m³) |
|---|---|
| Quartz / sand | 2650 |
| Calcite | 2710 |
| Water droplet | 998 |
| Iron / steel | 7870 |
| Alumina | 3970 |
| Coal dust | 1350 |
Stokes' law is used in sedimentation analysis, particle sizing (Andreasen pipette), centrifugal separation, and aerosol dynamics. Drag force grows linearly with velocity (unlike high-Re flow where it grows with V²).