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The Straight Dope



A coworker and I are arguing about the following riddle. I hoped you could give me a hand. A magician must cross a bridge carrying three gold pieces. He weighs exactly 68 kilograms, and each piece of gold weighs one kilogram. The bridge can carry no more than 70 kilograms or it will break. How does he cross the bridge safely, without throwing or dragging the gold across?

The answer supplied with the puzzle says he juggles the gold pieces and therefore never weighs more than 70 kg, because one of the gold pieces is in the air at all times. I disagree--the magician and his gold pieces make up a system that weighs an average of 71 kg, whether he throws and catches them or just carries them. What do you think? --DML, via the Internet

I think anybody carting around three kilos of gold (approximate value $41,000) can probably afford to find himself a better bridge. Maybe not the answer you were looking for, but somebody has to keep an eye out for the practical stuff.

Cecil has given some thought to offering a rigorous mathematical analysis showing that the downward force exerted on the bridge by the magician and his gold is, as you rightly surmise, 71 kg on average. I realize technically you're supposed to express force in terms of newtons rather than kilograms. I also realize I'm trying to communicate with the general public, much of which is, let's face it, mathematically challenged. I recall a conversation many years ago with a student at Northwestern who was convinced her fellow students were dopes. "Do you realize," she said indignantly, "that half the people in this place scored below the median?"

So let's skip the math and keep it simple. Suppose we accept the proposition that a juggling magician weighs only 70 kg because "one of the gold pieces is in the air at all times." This is equivalent to saying that the magician walks across the bridge with two gold pieces in his pockets and the third floating over his head.

Well, you did say he was a magician. But if we rule out the supernatural it's obvious the magician has to support that third gold piece somehow, yes? (Please say yes. I want to believe there's hope.) However he does it, he increases his weight by the weight of the gold. Stay off that bridge.


As one of your faithful but know-it-all-too-just-not-as-witty-by-half readers, I have a comment on your column about increased flatulence at high altitude [April 12]. Atmospheric pressure drops to half of sea level at about 18,000 feet, so that trapped gases double in volume. Having flown thousands of flights in unpressurized planes and in altitude chambers, experience tells my nose when we go over about 25,000 feet. Good check for oxygen mask fit. Your reader, however, was suffering from transverse incarcerated farts at 9,000 feet. That's about 72 percent of sea-level pressure, and thus gas expands by about 39 percent--a small diameter increase. I suspect Bacchus and Eros [the original writer complained about flatulence while spooning in a mountaintop cabin] affected this fellow much more than Charles' Law. --AJP, senior flight surgeon and general BSer, via the Internet

Booze plus lust is a major cause of flatulence? Remind me never to accompany you to a singles bar.

It may be true that when strapped into a cockpit you don't get noticeable, how shall we say, liberation of gas until above 25,000 feet. However, when you have sex you move around, or at least most people move around, thereby increasing opportunities for gas to escape. So it seems reasonable intestinal distension at 9,000 feet might lead to an attack of the toots.

Maybe you're not buying this, but goddamit, I'm trying to apply some science to the situation. Luckily we don't need to depend entirely on theory. See below.

[Flatulence] is a well-known phenomenon among skydivers. Crowded into a tight aircraft, as you pass between 6,000 and 8,000 feet, there is a good chance someone will let rip. We just consider it a recreational hazard. --L.V., via the Internet

So what do you think, doc? Skydiving being what it is, Cecil cheerfully admits that increased flatulence may be partly due to your being in a state of generalized muscular tension. But isn't that pretty much what happens during sex?


Is there something you need to get straight? Cecil Adams can deliver the Straight Dope on any topic. Write Cecil Adams at the Chicago Reader, 11 E. Illinois, Chicago 60611, or E-mail him at

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

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