"Where would the scale tip? On the left is a steel ball, on the right a ping-pong ball," Reddit user Veiy wrote, posing the conundrum. "I think the scale would raise to the right since the [buoyancy] ...

Rare souvenir: Sold in 1936, this ping-pong ball flew across the Atlantic—twice—with Dick Merrill. Where are all the ping-pong balls that aviation legend Dick Merrill stuffed in the wings of a ...