🟠 Terminal velocity — drag climbs with speed until the net force is zero

A sphere sinking through a viscous liquid feels weight down, buoyancy up, and Stokes drag up. Drag grows with speed, so the sphere accelerates only until the three balance; after that it falls at the steady terminal velocity v_t = 2a²(ρ−σ)g / 9η.

Walkthrough 1 / 3

Release the sphere: at first only weight and buoyancy act, so it accelerates downward.

Sphere radius a 1.0 mm

Viscosity η 0.50 Pa·s

v_t = 2a²(ρ−σ)g / 9η = — m/s · current speed v = — m/s
weight (down) = drag + buoyancy (up) once v = v_t

Animation speed 1.0×