Stokes' Law Calculator

It applies to small spherical particles settling slowly through a viscous fluid in smooth, laminar flow, such as fine silt in water. It breaks down for larger or faster particles.

A negative terminal velocity means the particle is less dense than the fluid and rises rather than sinks, like an air bubble in water or a foam bead in oil. The magnitude of the velocity is the same in both directions - only the sign flips. In practice, Stokes' Law applies only at low Reynolds numbers (Re < 1); for larger particles or faster flows, drag becomes non-linear and the Stokes formula underestimates drag, giving an overestimate of terminal velocity.