下雨了到底用走还是用跑的?

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、下雨的日子里，当你忘记带你的雨衣或雨伞而又想要尽量保持干爽时，你应该用走的，在雨中待上更多时间？或是你应该用跑的，同时也代表你会淋到更多侧边的雨滴？假设你还没有完全湿透，也不会跳进水坑。答案很简单，当你从一滴雨滴下移开，你也同时移入另一雨滴的路径。所以淋到你头顶的雨水量是固定的，不管你移动有多快。

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.

想要了解这个，你可以想象雨滴本身是静止的，而你和脚下的土地在雨中向上移动。而由于平行六面体（也就是个立体的平行四边形）的体积完全不取决于它的倾斜度，于是不管你平行移动得多快，每秒一样的雨量将会落在你的头顶上。现在，如果你不移动，从上方来的雨就是所有你会淋到的。但是如果你在移动，你也将会碰上来自侧边的雨滴，并且变得更湿。

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.

所以在任何一秒钟，站者不动可以让你保持最为干燥，而你移动的越快，就会变得越湿。但如果你试着从A地到达B地，那么站着不会给你多大的帮助。在A地到B地的路途上，你从侧边碰上的总雨量跟你移动的多快完全没有关系，就像是为何铲雪车不论行驶的确切速度，在一段路程上将会铲等量的雪。

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.

在雨中跑步的这种情况下，你可以再次使用平行六面体来理解。所以在一段特定时间内，相同的雨量将会从上方淋到你身上，不管你移动的多快。而在一段特定距离内，你会从侧边淋到相同的雨量–同样的，不管你移动的多快。

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.

所以你总共的淋湿程度等于每秒从顶端来的雨水造成之淋湿程度乘上你在雨中的时间，加上每公尺从侧边来的雨水造成之淋湿程度乘上你移动的公尺数。所以若要从一地到另一地时保持最为干爽，你应该试着减少从上方落到身上的水量。而很简单的，那意味着要尽快离开雨中。