A stalactite in a cave has drops of water falling from it to the cave floor below. The drops are equally spaced in time and come in rapid succession, so that at any given moment there are many drops in midair.

(a) Is the center of mass of the midair drops higher than, lower than, or equal to the halfway distance between the tip of the stalactite and the cave floor?

(b) Choose the best explanation from among the following:

I. The drops bunch up as they near the floor of the cave.

II. The drops are equally spaced as they fall, since they are released at equal times.

III. Though equally spaced in time, the drops are closer together higher up.