 Solution

On a moving step, the largest speed resolved by the discrete model is the distance per interval,This is a step-averaged speed; the model does not specify motion within the interval. Use the cell length $a=2r=20\mu \mathrm{m}=2.0\times 10^{-3}\mathrm{cm}$ in the stated Reynolds number formula. In consistent centimetre–gram–second units,Thus viscous effects dominate inertia overwhelmingly. The surrounding flow is in the Stokes flow regime: sustained movement needs applied forces, and inertial coasting is negligible. Using radius rather than the specified length as the characteristic size would halve the Reynolds number, without changing that physical conclusion.