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 and 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 walk or run in the rain?
Naturally, greater brains than mine have pondered this question and there are, obviously, two approaches that 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 two members of the National Climatic Data Center in the States, Thomas Peterson and Trevor Wallis. Naturally, they required a rainy day to conduct their experiment and 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 100 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 them. Peterson’s clothing had absorbed 7.5 ounces of water whereas Wallis’ had sucked up just 4.5. The obvious conclusion from the empiricists was that you got 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 the Harvard mathematician, David E Bell, who published in 1976 in the Mathematical Gazette what many consider to be the definitive analysis. 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. If the wind is blowing from behind you, the optimal speed at which you should run to minimise the amount by which you are wet is the speed of the wind.
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 – I make no allowances for the use of illegal stimulants – would only reduce your soaking by 10%.
Of course, as long as there is a problem, people will always take contrary stances. A physicist of the University of Udine in Italy, Alessandro de Angelis, in an article in the Discovery magazine espoused an alternative interpretation. He calculated, although my researches have failed to unearth the formula he used, 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 – that is a cracking pace in my view – the sprinter will only be 10% drier. Ergo running isn’t worth the bother.
A conclusion I have a lot of sympathy with 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.
But at least we now know!