I’m sure you’ve been there too. You are out for a walk without a jacket or an umbrella, and what was a bright blue sky when you set out suddenly turns grey. It starts to rain.
What to do? You either run to the nearest shelter and wait until the shower passes over, or you carry on, curse your stupidity for not bringing an umbrella, and get wet. An everyday scenario for sure, but for the enquiring mind, it poses a very real question: Do you get wetter if you run or walk in the rain?
Naturally, greater brains than mine have pondered this question. Two obvious approaches can be adopted to derive the truth: the empirical and the abstract. Let’s deal with the empirical first. I am indebted to the ever popular journal Health for this account of an experiment conducted by Thomas Peterson and Trevor Wallis, two members of the National Climatic Data Center in the United States.
Naturally, they required a rainy day to conduct their experiment. When conditions were judged to be ideal, they put on identical track suits and hats. To prevent their underwear from absorbing any of the rainwater and thereby invalidating the results, they wore plastic rubbish bags underneath their trackies.
Having identified earlier a suitable hundred-metre course, they set off, Peterson walking and Wallis running.
Once they had completed their course and had got back into the dry, they removed their outer clothing and weighed it. Peterson’s clothing had absorbed 7.5 ounces of water whereas Wallis’s had sucked up just 4.5 ounces. The obvious conclusion from the empiricists was that you get wetter walking in the rain than running.
And now to the more rigorous scientific approach. The bellwether for the algebraic approach to answering our poser is Harvard mathematician David E Bell, who published what many consider to be the definitive analysis in the Mathematical Gazette in 1976.
He developed an algebraic formula, fearsome to the untrained eye, which (if I am correct in my interpretation) suggests that if the rain is falling vertically or the wind is blowing in your face, you should run. Indeed, the faster you run, the less wet you will be over a defined distance.
Yet if the wind is blowing from behind you, things change. The optimal speed at which you should run to minimise how wet you get is the speed of the wind. ‘The solution is to keep pace with the wind if it is from behind; otherwise, run for it,’ was Bell’s conclusion.
In case you think that you need to emulate Usain Bolt to reduce the extent of your soaking, Bell’s formula suggests that running at what would be an Olympic record-breaking pace (making no allowance for the use of illegal stimulants) would reduce your soaking by only 10 per cent.
Of course, as long as there is a problem, people will always take contrary stances. Alessandro de Angelis, a physicist at the University of Udine in Italy, espoused an alternative interpretation in an article in Discovery magazine. Although my research has failed to unearth the formula he used, he calculated that when you compare a sprinter who runs at 22.4 miles per hour with a walker who goes at 6.7 miles an hour – a cracking pace, in my view, since most people naturally walk at around 3mph – the sprinter will be only 10 per cent drier. Ergo running isn’t worth the bother.
This is a conclusion I have a lot of empathy for as any form of energetic exercise is anathema to me.
So next time I’m out and get caught by a shower, I shall just curse my stupidity for forgetting my umbrella and carry on my merry way. I’m going to get wet whether I run or walk, and to reduce the degree of my soaking by expending unnecessary energy just doesn’t seem worth it.
Martin Fone is author of 'Fifty Curious Questions', from which this piece is an excerpt – find out more about his book or you can order a copy via Amazon.
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