下雨了到底用走還是用跑的?大綱

On those cold, rainy days when you forget your rain jacket or umbrella, and you want to stay as dry as possible, should you walk and spend more time in the rain? Or should you run, which means you’ll be hitting more rain drops from the side? Assuming you haven’t been fully soaked yet, and you aren’t jumping into the puddles. The answer is simple. As you move out of the way of one falling raindrop, you move into the way of another. So the amount of the rain hitting the top of you is constant, regardless of how fast you’re going.

在那些寒冷、下雨的日子裏，當你忘記帶你的雨衣或雨傘而又想要儘量保持乾爽時，你應該用走的，在雨中待上更多時間？或是你應該用跑的，同時也代表你會淋到更多側邊的雨滴？假設你還沒有完全溼透，也不會跳進水坑。答案很簡單，當你從一滴雨滴下移開，你也同時移入另一雨滴的路徑。所以淋到你頭頂的雨水量是固定的，不管你移動有多快。

To see this, you can picture that the raindrop themselves are stationary, and you and the earth beneath you are moving upwards through the rain. And since the volume of a parallelepiped (that’s a 3D parallelogram) doesn’t depend at all on its slant, then no matter how fast you’re moving horizontally, the same amount of rain will land on top of you each second. Now, if you’re not moving, the rain from the top is all you’ll get. But if you are moving, you’ll also run into raindrops from the side, and you’ll get wetter.

想要了解這個，你可以想象雨滴本身是靜止的，而你和腳下的土地在雨中向上移動。而由於平行六面體（也就是個立體的平行四邊形）的體積完全不取決於它的傾斜度，於是不管你平行移動得多快，每秒一樣的雨量將會落在你的頭頂上。現在，如果你不移動，從上方來的雨就是所有你會淋到的。但是如果你在移動，你也將會碰上來自側邊的雨滴，並且變得更溼。

So in any given second, you stay driest by standing still, and the faster you move the wetter you become. But if you’re trying to get from point A to point B, then standing still won’t do you much good. And en route from point A to point B, the total amount of rain you run into from the side has nothing to do with how fast you’re going, just like how a snowplow will plow the same amount of snow from a stretch of road, regardless of the exact speed it drives.

所以在任何一秒鐘，站者不動可以讓你保持最爲乾燥，而你移動的越快，就會變得越溼。但如果你試着從A地到達B地，那麼站着不會給你多大的幫助。在A地到B地的路途上，你從側邊碰上的總雨量跟你移動的多快完全沒有關係，就像是爲何鏟雪車不論行駛的確切速度，在一段路程上將會鏟等量的雪。

In the case of running through the rain, you can figure that out using parallelepipeds again. So over a given period of time, the same amount of rain will hit you from the top, regardless of how fast you’re going. And over a given distance, you’ll hit the same amount of rain from the side — again, regardless of how fast you’re going.

在雨中跑步的這種情況下，你可以再次使用平行六面體來理解。所以在一段特定時間內，相同的雨量將會從上方淋到你身上，不管你移動的多快。而在一段特定距離內，你會從側邊淋到相同的雨量–同樣的，不管你移動的多快。

So your total wetness is equal to the wetness per second for rain from the top times the amount of time you spend in the rain, plus the wetness per meter for rain from the side times the number of meters you travel. So to stay driest getting from one point to another, you should try to minimize the amount of water falling on to you from above. And quite simply, that means getting out of the rain as fast as possible.

所以你總共的淋溼程度等於每秒從頂端來的雨水造成之淋溼程度乘上你在雨中的時間，加上每公尺從側邊來的雨水造成之淋溼程度乘上你移動的公尺數。所以若要從一地到另一地時保持最爲乾爽，你應該試着減少從上方落到身上的水量。而很簡單的，那意味着要儘快離開雨中。