Stokes’ law : If a fluid flows past a sphere or a sphere moves through a fluid, for small enough
∴ Viscous force = gravitational force-buoyant force
= mg – mLg
where m = mass of the sphere = \(\frac43\)\(\pi\)r3ρ and mL</sub. = mass of the liquid displaced = \(\frac43\)\(\pi\)r3ρL.
At its terminal speed vt, the magnitude of the viscous force by Stokes’ law is
[Note : Theoretically, v → vt as time t → ∞. In practice, if η is appreciable, then vt tends to v in a very small time interval.]
[Data: g = 9.8 m/s2]
