Question:

What weighs more on the moon than on the earth?

.

.

C

A

P

T

A

I

N

I

N

T

E

R

V

I

E

W

.

.

Solution: Let’s consider two excellent responses, one literal, one figurative. First the literal. It takes a special mentality to move from one critical difference to consider what other differences may apply. In this case, the salient difference is that the moon has less gravity than the earth. True enough. But don’t stop there. What other differences exist? Earth has an atmosphere and the moon does not. And what is one property of an atmosphere? It provides buoyancy. Things with definite mass definitely float on the earth and therefore have no weight. So, on the moon, any balloon filled with a lighter-than-air gas, such as helium or hydrogen, would work for an answer.

Some people may object that the balloon would nevertheless weigh as much on the moon as on earth. Granted the mass of the balloon remains unchanged, but weight is something else. On earth, helium balloons don’t weigh anything because the atmosphere supports them. If you tried to put a helium-filled balloon on a scale, no weight would register because the buoyancy of the balloon is greater than the pull of gravity on the balloon. But on the moon, the moon’s gravity would definitely pull it against a scale. Therefore, on the moon the balloon will actually register some weight, even with the moon’s gravity one-sixth that of earth.

Extra credit: Note that it would be impossible to conduct this experiment. No inflatable balloon can exist on the moon or in a vacuum, as it will immediately explode.

Now a stunning metaphorical response voiced by my friend David Jones of Evanston, Illinois, proving that with the right attitude, every “technical” puzzle permits a satisfying nontechnical response:

What weighs more on the moon than on the earth? The conscience of an astronaut, if the astronaut left for the moon on the morning of his wife’s birthday and he forgot to acknowledge it.

Answer: Any lighter-than-air balloon or the conscience of an astronaut.