We release an oil drop of radius r in air. The density of the oil is 640 kg/m3. C1 and C2 for 1 atmosphere air at 20∘ C are 3.90 × 10−4 (kg/m)/sec and 0.73 kg/m3, respectively.

Question

How small should the oil drop be so that the drag force is dominated by the linear term in the speed (in lectures we called this Regime I). In this regime, the terminal velocity is mg/C1r. [m is the mass of the drop].

r<<