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The Straight Dope



Jumpin' Jack and Lazy Jim, twins, emerge from a fancy restaurant only to find all the valets have split and a heavy rainstorm lies between them and their car, 100 yards away. Jumpin' Jack bets Lazy Jim that if he runs and Jim walks, he will arrive at the car not only faster but drier. Jim accepts the bet, arguing that Jack's broad chest will run into more raindrops than will hit Jim on the top of his slow-moving but small head. Who wins the bet? If distance and rain density are important to figuring the answer, please provide us with a handy wallet chart so we may know when to be nimble and when not. Meanwhile, I'll place my bet with Jack. --Ryan Kuhn, Chicago

You're obviously a sensible young man, which is more than I can say for some of the bozos out there. According to Discover magazine, Alessandro De Angelis, a physicist at the University of Udine, Italy, calculated some years ago that "a sprinter racing along at 22.4 miles an hour does get less wet, but only 10 percent less wet, than a hasty stroller (6.7 miles an hour)." Conclusion: running isn't worth the trouble.

I haven't been able to find the original paper, if any, on which this report was based, so I don't know how De Angelis arrived at his conclusion. Not that it matters. Neither theory nor experiment (mine) bears out his crackbrain view. Running through the rain will keep you a lot drier (not just 10 percent drier) than walking.

First the theory. We divide the raindrops hitting you into two categories: (1) head drops, which fall from above and would hit you even if you were standing still, and (2) chest drops, which you run or walk into and which wouldn't hit you if you were standing still. We can all agree that the number of head drops is strictly a function of how long you're out in the rain; if you run, fewer head drops. The question is whether the allegedly larger number of chest drops you get when running outweighs the definitely larger number of head drops you get while walking.

Not to keep you in suspense, the answer is no. If we ignore aerodynamic effects, we can show mathematically (but won't) that while you'll collect many fewer head drops running rather than walking, you'll get exactly the same number of chest drops, regardless of the speed at which you travel. Bottom line: you'll be a lot wetter if you walk.

But wait, you say. What about those pesky aerodynamic effects? The requisite math is a bit daunting, but never fear. Heedless of his delicate health or his already low reputation with the neighbors, your columnist spent a recent rainy Saturday running down the street like an idiot brandishing pieces of red construction paper clipped to cardboard, the better to snag and count raindrops. Methodology: three trials of two runs each over a fixed distance, once running, once walking. Winds: calm. Angle of attack of paper relative to ground: 45 degrees. Results:

Trial #1. Running, 15 seconds to run course; 213 drops. Walking, 40 seconds; couldn't count drops, paper soaked. Shortened course.

Trial #2. Running, 7 seconds; 131 drops. Walking, 20 seconds; 216 drops.

Trial #3. Running, 7 seconds; 147 drops. Walking, 17 seconds; 221 drops.

So there you are. The differences are larger than the numbers suggest because many drops on the "walking" papers dried before I could count them. My guess is that the number of drops is exactly proportional. If you're out twice as long, you get twice as wet.

One obvious caveat. If enough rain falls on you, whether because of the intensity of the rainfall or the distance you have to travel, eventually you'll be thoroughly soaked. After that it doesn't matter whether you run or walk; you're as wet as you're going to get. So the preceding applies only to relatively short sprints through less-than-torrential downpours. Sorry, no wallet charts. My advice: always run--if nothing else you could use the exercise.

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

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