《那些古怪又讓人憂心的問題》第115期:無重力射箭(2)
Once the arrow leaves that range, it's no longer particularly dangerous . . . but it's not even close to stopping.
After five minutes, the arrow would have flown about a mile, and it would have slowed to roughly walking speed. At that speed, it would experience very little drag; it would just cruise along, slowing down very gradually.
5分鐘後，箭支已經飛出了大約1英里（約1.6千米），速度也下降到了步行速度。以這個速度飛行只會受到非常小的阻力，因而箭支會繼續“滑行”，並緩慢地減速。At this point, it would have gone much farther than any Earth arrow can go. High-end bows can shoot an arrow a distance of a couple hundred meters over flat ground, but the world record for a hand bow-and-arrow shot is just over a kilometer.
到了現在，這支箭飛出的距離已經超過地球上任何一支箭的射程了。高端的弓能在平地上將箭射出幾百米，不過手持弓的最遠射程世界紀錄略高於1千米。
This record was set in 1987 by archer Don Brown. Brown set his record by firing slender metal rods from a terrifying contraption that only vaguely resembled a traditional bow.
這個紀錄由射手丹•布朗於1987年創立，他用一個幾乎已經沒有弓的樣子的可怕裝置將細長的金屬桿射出了世界紀錄。As the minutes stretch into hours and the arrow slows down more and more, the airflow changes.
隨着時間越來越長，箭支的飛行速度越來越慢，此時流經箭支表面的氣流開始發生變化。Air has very little viscosity. That is, it's not gooey. That means things flying through the air experience drag because of the momentum of the air they're shoving out of the way-not from cohesion between the air molecules. It's more like pushing your hand through a bathtub full of water than a bathtub full of honey.
空氣的黏度很小，也就是說沒有黏黏的感覺。這意味着飛過空氣的物體受到的空氣阻力來自於它們排開空氣的動量——而不是來自於物體與空氣分子之間的黏力。這像是你用手推過一浴缸的水而非蜂蜜。After a few hours, the arrow would be moving so slowly that it would be barely visible. At this point, assuming the air is relatively still, the air would start acting like honey instead of water. And the arrow would, very gradually, come to a stop.
幾個小時後，箭支的飛行速度已經到了肉眼幾乎無法分辨的程度。假設此時空氣是相對靜止的，那麼現在空氣對於箭支更像是蜂蜜那樣黏糊糊的，而箭支也會慢慢地趨向停止。The exact range would depend heavily on the precise design of the arrow. Small differences in an arrow's shape can dramatically change the nature of the airflow over it at low speeds. But at minimum, it would probably fly several kilometers, and could conceivably go as far as 5 or 10.
箭支的外形細節會大幅影響最終的射程。箭支形狀的細小差別會極大改變低速流過的空氣的特性，但此時箭支至少已經飛出了好幾千米，飛出個5千米或者10千米也是可以想象的。Here's the problem: Currently, the only sustained zero-g environment with an Earth-like atmosphere is the International Space Station. And the largest ISS module, Kibo, is only 10 meters long.
現在問題來了：目前能夠持續維持零重力的類地環境只存在於國際空間站。國際空間站最大的一個單元“希望號實驗室”的長度也只有10米。This means that if you actually performed this experiment, the arrow would fly no more than 10 meters. Then, it would either come to a stop . . . or really ruin someone's day.
這意味着如果你真的打算做這個實驗，箭支飛不出10米。之後這支箭要麼就此停下來，要麼就釀成大禍。1 Also, you don't usually shoot astronauts with a bow and arrow - at least not for an undergraduate degree.
1． 而且你不太會沒事兒去拿箭射宇航員，至少一個有學士學位的人不會這麼幹。
