CONDITION FOR OCCURENCE OF CIRCULAR PENETRATION DURING IMPACT OF A FALLING DROPLET WITH A FLUID

In observing the impact of a free falling droplet with a fluid, Cai discovered what he called the circular penetration phenomenon, whose occurence had a periodic dependence on the height of free fall. Empirical formulas were developed by Cai to correlate his experimental measurements. This note shows that formulas in better agreement with experiment can be derived from the theory of free oscillation of droplets, thus providing a physical basis for circular penetration.