A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Which will keep you drier, running through the rain or walking?

October 16, 1992

Dear Cecil:

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.

Cecil replies:

You're obviously a sensible young man, which is more than I can say for some of the people who have looked into this. 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% 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/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.

You can fool some of the people some of the time

Dear Cecil:

I enjoyed your column about whether we get less wet running or walking in the rain. I was particularly impressed with your initiative in collecting data. Regrettably, some tests of statistical significance I performed on the data you supplied seem to poop the party: [two pages of incomprehensible mathematical symbols follow]. I know your data look convincing to the untrained eye, but a statistician they smack of the problem of small numbers. Next time invest in a few extra sheets of construction paper and improve your significance level.

Cecil replies:

Your argument, Catherine, is that two trials isn't a large enough sample to base any firm conclusions on. Cecil knows this. Cecil also knows that if he doesn't get his column in on time, a chancy proposition under the best of circumstances, he may eventually be informed the time has come for him to get a real job. So he takes certain shortcuts. But your point is well taken. Next time I need somebody to dash through the drink a few dozen times, I'll give you a call.

Cecil's findings confirmed!

Thomas Peterson and Trevor Wallis of the National Climatic Data Center, writing in the meteorological journal Weather, also tackled the running vs. walking controversy. "We decided to deal with this with scientific rigor. We did an experiment," Peterson was quoted as saying in Health magazine.

The magazine goes on to describe the experiment: "One rainy day the two men donned identical sweat suits and hats, which they'd weighed before the test. For added accuracy, they wore plastic garbage bags underneath the sweat suits to keep their underclothes from wicking away any water. They then set out through the downpour on a 100-meter course. Wallas ran; Peterson walked.

"When they finished, the men weighed their clothes again to find out how much water they'd soaked up. Peterson's had absorbed about seven and half ounces, while Wallis's sopped up only four and a half."

In short, running will keep you drier than walking. Told ya.

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