Stokes' Law (F = 6πηav)
jee-mainjee-advancedneet-ug
F = 6πηav
What each symbol means
| Symbol | What it stands for |
|---|---|
| F | Viscous drag force on the sphere (N) |
| a | Radius of the sphere (m) |
| v | Velocity of the sphere relative to fluid (m/s) |
| η | Coefficient of viscosity of the fluid (Pa·s) |
When to use this
Valid for a smooth sphere moving slowly through a viscous fluid (low Reynolds number, laminar flow). Force is proportional to velocity (retarding force). Applies to falling raindrops, sedimenting particles. Assumes sphere is small and speed is not too high.