Originally Posted by Hondo6

From what you said above, it appeared to me you didn't realize that a stationary (with respect to linear motion) object that is rotating has rotational inertia. Because otherwise it's hard to see how you missed [MENTION=23624]Trakhak[/MENTION] 's analogy, even if the scenario he presented could be better.



Here's how this relates: at the time of impact with the water, both the ping-pong ball and the bearing ball will have linear momentum (a quantification of its inertia at a given velocity) and linear kinetic energy due to the uniform acceleration of gravity minus aerodynamic drag. Each must shed all of their kinetic energy - and thus momentum - prior to coming to a stop.

Since the items here are of similar size, aerodynamic forces acting on each over a 12" drop would be roughly the same. The relative depth each achieved before stopping would indicate which had the greater kinetic energy (and thus momentum) at time of impact with the water's surface.

Unfortunately, in Trakhak's example the steel ball won't ever be stopped completely because it is denser than water. It will thus and will continue to sink after shedding the kinetic energy acquired before striking the surface.

Had he used a smooth oak sphere (density approx 0.6 to 0.9 g/cm3, depending on variety) the size of a ping-pong ball instead of a steel bearing ball of that size, the analogy might have been easier to grasp. In this revised scenario, both the wooden sphere and ping-pong ball would stop after hitting the water, then float afterwards. But the oak sphere, being far denser, would penetrate the surface to an appreciably greater depth than the ping-pong ball due to its greater momentum and kinetic energy at time of impact. The approximate difference could be determined by measuring the max depth reached by each and comparing them.