I read with interest Carl Mungan’s letter to the editor.1 He gave an alternate way of looking at the problem posed in the January 2016 “Figuring Physics” column2 concerning a ping-pong ball tethered internally underwater and an equal-sized lead ball externally supported underwater, both in identical beakers containing equal amounts of water placed on opposite sides of a balance. Mungan cleverly pointed out that the tethered ping-pong ball was pulling up on the bottom of the beaker, thereby reducing its weight.
Another way of looking at the problem is to start with two beakers of water, equally filled partway but with no balls in either of them, balancing on a scale. Now freely float a ping-pong ball on the surface. In that mode it is displacing its weight in water, which is manifested by a rise in water level; however, this rise is not as great as the...