Have you ever dashed across a parking lot in a sudden rainstorm? You might think that you'll stay drier by running as fast as you can‑‑but wait‑‑the faster you run, the more drops you'll run into horizontally, soaking your front.
You want to stay as dry as possible, so what should you do: Walk or run?
The Scientists Perspective
A scientist would break this problem into its simplest elements. If there's no wind, you'll only get wet from two directions‑‑above as the drops fall on you, and in front as you move into them. The amount of wetness from above is determined by how long you stay in the rain.
If you stay outside twice as long, your head and shoulders will get twice as wet. As far as your top is concerned, the faster you run the better. Running faster means less time spent in the rain.
The water you run into is another story. The faster you go, the more rapidly your front will collide with raindrops, but you'll also spend less time running through them.
As it turns out, no matter how fast you go, you'll always hit the same number of drops from the front. If you slow down, you'll hit them more slowly, but the total amount will be the same at the end of your trip.
Putting the two parts together‑‑top and front‑‑it's clear that running will indeed keep you drier than walking, but not by very much. It only keeps the top of your head and shoulders drier. Your front will be just as wet whether you sprint or shuffle.