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In the summer of 1895, crowds flooded the Coney Island boardwalk to see the latest marvel of roller coaster technology: the Flip Flap Railway.
1895年夏天，人群涌向康尼岛栈道，大家都来观看最新最神奇的过山车技术：翻转火车。
This was America's first-ever looping coaster -- but its thrilling flip came at a price.
这是美国首个拥有环状结构的过山车，但是它带来的惊险刺激是有代价的。
The ride caused numerous cases of severe whiplash, neck injury and even ejections, all due to its signature loop.
乘坐过山车造成了不计其数的严重鞭伤颈部受伤，甚至是更严重的弹射，而这都是环状结构造成的。
Today, coasters can pull off far more exciting tricks, without resorting to the "thrill" of a hospital visit.
如今，过山车有更多刺激的玩法，人们也不会因此受伤就医。
But what exactly are roller coasters doing to your body, and how have they managed to get scarier and safer at the same time?
但是过山车会对身体造成什么影响呢，它如何在保证刺激的同时保障安全呢？
At the center of every roller coaster design is gravity.
每个过山车的设计核心都是重力。
Unlike cars or transit trains, most coasters are propelled around their tracks almost entirely by gravitational energy.
与汽车和火车不同，大多数过山车都沿着轨道几乎全部靠重力驱动。
After the coaster crests the initial lift hill,
在过山车到达第一个顶峰时，
it begins an expertly engineered cycle -- building potential energy on ascents and expending kinetic energy on descents.
它便开始了一个工程力学循环--在上升时积累势能，在下降时释放转换为动能。
This rhythm repeats throughout the ride, acting out the coaster engineer's choreographed dance of gravitational energy.
这种循环在整个过程中重复，这是由过山车设计者编排的一组重力舞蹈演出。
But there's a key variable in this cycle that wasn't always so carefully considered: you.
但是在这个循环中有一个因素没有被考虑进来：那就是你。
In the days of the Flip-Flap, ride designers were most concerned with coasters getting stuck somewhere along the track.
在翻转过山车的时代，过山车设计者们最担心的是过山车会在轨道的某处卡住。
This led early builders to overcompensate, hurling trains down hills and pulling on the brakes when they reached the station.
因此早期的过山车建造者们用力过猛，让车体在下坡时猛冲，在车体到达终点时使用刹车系统。
But as gravity affects the cars, it also affects the passengers.
但是重力既会作用于车体，也会对乘客施加影响。
And under the intense conditions of a coaster, gravity's effects are multiplied.
在过山车激烈的运动下，重力的影响成倍放大。
There's a common unit used by jet pilots, astronauts, and coaster designers called "g force".
飞行员、宇航员以及过山车设计者经常使用的一个用来衡量力大小的单位G力（重力加速度）。
One G force is the familiar tug of gravity you feel when standing on Earth -- this is the force of Earth's gravitational pull on our bodies.
一个G力等于人站在地球上感受到的重力，这是地球作用在我们身上的引力。
But as riders accelerate and decelerate, they experience more or less gravitational force.
但是随着过山车乘客的加速和减速，他们实际感受到的重力会偏大或偏小。
Modern ride designers know that the body can handle up to roughly 5 Gs, but the Flip-Flap and its contemporaries routinely reached up to 12 Gs.
现代过山车设计者已知人类身体大概可以承受5个G力，但是翻转火车和同时代其他过山车通常可以达到12个G力。
At those levels of gravitational pressure, blood is sent flying from your brain to your feet,
在这样的重力水平下，血液会从大脑飞速涌向双脚，
leading to light-headedness or blackouts as the brain struggles to stay conscious.
大脑为了努力保持清醒，会出现轻微头晕或暂时性晕厥。
And oxygen deprivation in the retinal cells impairs their ability to process light, causing greyed out vision or temporary blindness.
同时，视网膜缺氧也会让感光能力受损，导致视物变灰或短暂失明。
If the riders are upside down, blood can flood the skull, causing a bout of crimson vision called a "redout".
如果乘客头朝下，大脑会出现充血，导致视觉变红，称为红视。
Conversely, negative G's create weightlessness.
相反，负重力会产生失重。
Within the body, short-term weightlessness is mostly harmless.
对身体来说，短期失重通常无害。
It can contribute to a rider's motion sickness by suspending the fluid in their inner ears which coordinates balance.
它会导致乘客的晕动症，原因在于，失重条件下内耳中负责协调平衡的液体流动受到限制。
But the bigger potential danger -- and thrill -- comes from what ride designers call airtime.
但还有更大的刺激，或是说潜在危险，过山车设计者们将其称为空中停留时间。
This is when riders typically experience seat separation, and, without the proper precautions, ejection.
这指的是乘客经常体会到的身体与座椅相分离的状态，如果没有恰当的预防措施乘客会被座椅弹射出来。
The numerous belts and harnesses of modern coasters have largely solved this issue,
现代过山车上数量众多的安全带在很大程度上规避了这个风险，
but the passenger's ever-changing position can make it difficult to determine what needs to be strapped down.
但是乘客姿势的不断变化会使得确定身体位移的难度增大。
Fortunately, modern ride designers are well aware of what your body, and the coaster, can handle.
幸运的是，现代过山车的设计者们都详细了解我们的身体和过山车能够承受什么样的影响。
Coaster engineers play these competing forces against each other, to relieve periods of intense pressure with periods of no pressure at all.
过山车工程师们把玩着这些彼此相互作用的力，通过无重力的阶段来释放重力。
And since a quick transition from positive to negative G-force can result in whiplash, headaches, and back and neck pain,
超重与失重的快速转变会导致鞭打一样的疼痛、头痛、后背和脖子的疼痛，
they avoid the extreme changes in speed and direction so common in thrill rides of old.
工程师们避免出现速度和方向的极限变化，而这些则在老式过山车中普遍存在。
Modern rides are also much sturdier, closely considering the amount of gravity they need to withstand.
现代过山车也更加坚固，设计时仔细考虑了整体装置的承重。
At 5 G's, your body feels 5 times heavier; so if you weigh 100lbs, you'd exert the weight of 500 lbs on the coaster.
在5个重力水平下，身体会感到原来的5倍重，如果你体重是100磅，你施加在过山车上的力会达到500磅。
Engineers have to account for the multiplied weight of every passenger when designing a coaster's supports.
工程师在设计过山车时需要考虑每位乘客重量的数倍。
Still, these rides aren't for everyone. The floods of adrenaline, light-headedness, and motion sickness aren't going anywhere soon.
但过山车并不适合所有人。肾上腺素的飙升，轻微的头痛以及运动带来的恶心依然会继续存在。
But today's redundant restraints, 3D modeling and simulation software have made roller coasters safer and more thrilling than ever.
但是如今的完备的安全措施，3D建模技术和模拟软件使得过山车更加安全，也更加刺激。
Our precise knowledge about the limits of the human body
我们对于人体极限的准确了解，
have helped us build coasters that are faster, taller, and loopier -- and all without going off the rails.
帮助我们将过山车设计得更快、更高、更险，当然都是在过山车体不离开轨道的前提下实现的。
