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HOCKEY PUCK
冰球一击
Q. How hard would a puck have to be shot tobe able to knock the goalie himself backward into the net?
Q．如果你想击出一颗冰球并指望它把对面守门员一起撞进球网里，那么你得花多少力气？
A. THIS CAN'T REALLY HAPPEN.
A．这不可能发生。
It's not just a problem of hitting the puckhard enough. This book isn't concerned with that kind of limitation. Humanswith sticks can't make a puck go much faster than about 50 meters per second,but we can assume this puck is launched by a hockey robot or an electric sledor a hypersonic light gas gun.
这不仅仅是你能拿出多大的力气去击球的问题，这本书可不关心那种限制。一个地球人用一根棍子没法击出时速远大于每秒50米的球，但我们总可以假设冰球是被一个冰球机器人，或者一个电动滑板，再或者是一个超音速轻气炮发射出来的。
The problem, in a nutshell, is that hockeyplayers are heavy and pucks are not. A goalie in full gear outweighs a puck bya factor of about 600. Even the fastest slap shot has less momentum than aten-year-old skating along at a mile per hour.
这个问题说到底就是冰球运动员太重，而冰球太轻。一个穿戴全副装备的守门员的重量是冰球的600倍左右，即便是以最快速度击出的冰球的动量也不超过一个10岁小孩儿以每小时1.6千米的速度滑冰时的动量。
Hockey players can also brace pretty hardagainst the ice. A player skating at full speed can stop in the space of a fewmeters, which means the force they're exerting on the ice is pretty substantial.(It also suggests that if you started to slowly rotate a hockey rink, it couldtilt up to 50 degrees before the players would all slide to one end. Clearly,experiments are needed to confirm this.)
冰球运动员踩在冰面上也相当稳。一个全速滑行的运动员能在几米距离内停下来，这意味着他与冰面之间的作用力相当可观。（这同时说明如果你慢慢抬起冰球场的一边，那么倾角需要达到50度才能让所有运动员滑到另一边去。显然，我们急需一场实验来验证这个说法。）
From estimates of collision speeds inhockey videos, and some guidance from a hockey player, I estimated that the165-gram puck would have to be moving somewhere between Mach 2 and Mach 8 toknock the goalie backward into the goal-faster if the goalie is bracing againstthe hit, and slower if the puck hits at an upward angle.
基于我对冰球视频中碰撞速度的估计，以及我的一位玩冰球的朋友给我的一些帮助，我推算出一个165克重的冰球需要以2～8马赫之间的速度运动才能使守门员被打进到网里——如果守门员稳稳地站在冰面上，速度要更高些，如果以向上的角度击打冰球的话速度会低一些。
Firing an object at Mach 8 is not, initself, very hard. One of the best methods for doing so is the aforementionedhypersonic gas gun, which is-at its core-the same mechanism a BB gun uses tofire BBs.
以8马赫的速度发射一个物体本质上来说不是很困难，要实现它最好的方法就是前面所说的超音速气炮，其实——就核心原理来说——它跟发射BB弹的BB枪没有区别。
