$2.1.39^*.$ The drag force of a liquid or gas, proportional to the square of the velocity of a moving body, is associated with the formation of vortices in the medium near the surface of this body. The drag force, which is proportional to the speed of a moving body, is associated with the slippage of the layers of the medium when it flows around this body. Both phenomena occur simultaneously. Why, however, can only one type of resistance be taken into account under certain conditions? Based on the data of the previous two problems, estimate at what value the product of the radius of a round drop and its velocity is, both types of air resistance are comparable in their effect on the movement of the drop.
This is related to the Reynolds number for a given situation.
If the Reynolds number $\text{Re}<2000$, then the drag force is proportional to the speed
If $\text{Re}>2000$, then the drag force is proportional to the square of the speed
NO: More about Reynolds numbers wikipedia.org