Do you get wetter if you run or walk in the rain?
Whether you walk or run, you're going to get wet, but there is an optimal speed to avoid the worst of it. The question is whether it's actually worth it.
Asked by: Sophie Hendren, by email
People still argue about this question, even though Harvard mathematician David Bell worked out the answer back in 1976. His answer was that if the rain is falling vertically, or there is a wind blowing in your face, you should run - and the faster you run, the less wet you will get over the same distance. If the wind is blowing from behind, you should still run, but now there is an optimum speed at which you will get least wet - the speed of the wind.
Bell's calculations (published in The Mathematical Gazette) needed only simple algebra, and it's surprising that the question is still argued over. Perhaps one reason is that, in practical terms, it doesn't really make much difference how fast you run. Even if you run at a world-record pace, his formula shows that you will only get 10 per cent less wet. Hardly worth the bother of running really.