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The Straight Dope


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While busily working one afternoon (aka staring at the clouds), my coworker told me that a cloud can weigh as much or more as a 747. I think she's nuts and that this is impossible. Please set her straight.

--JMG, via the Internet

Hope you didn't put serious money on this. The maximum takeoff gross weight of a 747 is 875,000 pounds. Did you know this includes six million parts? Three million of which are fasteners? One and a half million of which are rivets? The people at Boeing are crammed full of facts like this.

Anyway, let's be scientific and say a 747 weighs 400,000 kilograms. The amount of water vapor in clouds varies widely depending on temperature, barometric pressure, and other factors. However, five grams per cubic meter is about average. We feel confident in stating this number because it was confirmed for us by the meteorological office at the airport at the Isle of Man, off the coast of England. I'm telling you, our informants are everywhere. A good-sized cumulonimbus cloud (thunderhead) might be ten kilometers tall, with a base ten kilometers in diameter. Noodling a bit, we come up with a volume of 785 billion cubic meters per cloud (you can see this is not looking good), giving us a mass of roughly four billion kilograms per cloud, or the equivalent of not one but 10,000 747s.

To put it another way, a none-too-impressive cloud, one kilometer in diameter and 100 meters thick, has a mass equivalent to one 747. And they let these things just float around up there! Why, if one fell on us, it would...well, it would get really foggy, that's what. Now of course, it's true that weight isn't the same as mass, and that a cloud put on a scale wouldn't weigh anything. But still, there's a lot of stuff in those clouds. Think about it: suppose it's one of those dark, gray days, with cloud cover one kilometer thick. Suspended above your noggin (to be precise, above the one square meter centered on your person) is the equivalent of five kilograms (11 pounds) of water! And I'm just talking about the water that's condensed into clouds--there's a lot more if you count water vapor in general. If you feel a weight hanging over you during such weather, you've got good reason.

Why did Charles Manson believe that the Beatles song "Helter Skelter" was about the upcoming race war? Are there any documents that you own that say why in hell he would think this, other than the fact that he is crazy? --J.C. from MI

I'd say the fact that he's crazy pretty well covers it. "Helter Skelter," which appeared on the Beatles' White Album, was Paul McCartney's attempt to outrock Pete Townshend of the Who. Some Beatles fans describe the song as heavy metal, which is putting it a bit strongly. But it had more energy than most McCartney compositions of the period, and the descending refrain "helter skelter" somehow lent it an edginess that made it stick in the mind.

But "in England, home of the Beatles, 'helter skelter' is another name for a slide in an amusement park." (This from Helter Skelter, the best-selling book about the Manson murders by prosecutor Vincent Bugliosi.) The Oxford English Dictionary further clarifies that a helter skelter is "a towerlike structure used in funfairs and pleasure grounds, with an external spiral passage for sliding down on a mat." Recall the opening line: "When I get to the bottom I go back to the top of the slide / Where I stop and I turn and I go for a ride." It's a joke, get it? The Rolling Stones might do this faux bad-guy thing about putting a knife right down your throat, but the ever-whimsical McCartney figured he'd rock the house singing about playground equipment.

All this went over the head of Charles Manson. He thought Helter Skelter was the coming race war and the White Album was a call to arms. If you're in a certain frame of mind you can understand some of this, e.g., the "piggies" in the tune of the same name, who need a "damn good whacking," and the sounds of gunfire in "Revolution 9." But to think that the line "you were only waiting for this moment to arise" in the song "Blackbird" was an invitation to black people to start an insurrection...sure, Charlie. Whatever you say. Now put down that gun.


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