Stokes' Drag (F = 6πμrv)
Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!
Learning zone
At the scale of dust, droplets, and cells, fluids feel like honey: inertia is irrelevant and drag grows linearly with speed, viscosity, and size. This linearity is what gives small particles a terminal settling velocity — the workhorse of sedimentation basins in water treatment, of centrifuge protocols in the lab, and of Millikan's oil-drop experiment, which used Stokes' law to weigh single droplets and thereby measure the charge of the electron.
Stokes' Drag (F = 6πμrv)
Where
- = Drag force
- = Dynamic viscosity
- = Sphere radius
- = Speed
Missing one of these? Work it out first, then come back
- Drag force — Drag Force (F = ½CdρAv²), Newton's Second Law
- Dynamic viscosity — Reynolds Number, Poiseuille's Law
- Sphere radius — Poiseuille's Law, Centripetal Acceleration (a = v²/r)
- Speed — Speed, Distance & Time, Kinetic Energy