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The Straight Dope 

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What's this I hear about "crop circles" being mysteriously flattened in the corn and wheat fields in the English countryside around Stonehenge? I heard that attempts have been made to duplicate these circles without success. What's the Straight Dope? --Kimberly Moon, Dallas

Oh, God, not the alien spaceships again. According to a recent story in Skeptical Inquirer, about 165 of the flattened circles had been reported as of last year, some up to 150 feet in diameter. The stalks aren't broken, just bent over. The earliest circles were reported in 1948, but they've only become common in the last decade. Numerous explanations have been offered: snared animals running in circles, helicopters flying upside down, giant mushrooms, and, just to show you even crackpots read the newspapers, a hole in the ozone layer that allows ultraviolet radiation to fry the alfalfa.

A physicist blames the circles on "small, stationary wind vortices"; others predictably chalk them up to an unknown intelligence. Whatever the truth of the matter, at least some of the circles are probably hoaxes. Last fall the BBC, in the course of doing a report on the phenomenon, snuck a crew of wise guys into the middle of a field, making sure everybody walked in the tractor tracks so as not to leave footprints. The pranksters then formed a line, linked arms, and did a slo-mo shuffle somewhat reminiscent of a marching band on Valium. The result? A perfect circle. Too perfect, says one true believer. Uh-huh, says Cecil. Forgive me if I don't get too excited about these things, but it's been a long 18 years.

Jill and I walk every day on our lunch hour, so we see a lot of street and sidewalk repairing going on. What we'd like to know is, why do they put lines in cement sidewalks? They pour and smooth out a perfectly good sidewalk, then they draw lines in it. The lines only go a quarter-inch deep, so what good do they do? We remember the saying when we were kids, "step on a crack, break your mother's back"--do we have sadistic city employees? --Lorraine and Jill, Santa Barbara, California

Cecil was sure this was going to be another one of those "I dunno, we've always done it that way" questions, which have been turning up with dismaying regularity lately. But it turns out there's a good reason for the lines. Not that cement contractors necessarily know what it is, of course. Many of them have the idea that the lines allow the concrete to expand and contract with changes in temperature--not true, strictly speaking.

Concrete does expand and contract, and for that reason expansion joints, typically some sort of compressible fiber board, are put in every 40 feet or so. But the lines you're talking about, which are called "contraction joints," serve another, admittedly related, purpose. Concrete normally shrinks a bit as it dries, resulting in unsightly cracks. Cement finishers put in contraction joints so that when the concrete does crack, it'll do so at the contraction joints, where the slab is thinnest, rather than just any old place. That way it won't look so bad.

Unfortunately, the joints often don't work very well because the finishers don't make them deep enough. Ideally the joints should be at least 25 percent of the depth of the slab, meaning on a typical three-and-a-half-inch-thick sidewalk the lines should be at least seven-eighths of an inch deep. Anything less is just decoration. But do the construction workers listen when Cecil tries to counsel them on this subject? They do not. They make rude remarks. So much 'tude, so little respect--no wonder we have such problems in our society.

Has anyone ever had sex in space? If so, how was it? --Curious in North Dallas

Guess it kinda depends on what you mean by sex, don't it?

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

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