In the early 1960s, Dick Fosbury tried his hand at almost every sport,
20世纪60年代初，Dick Fosbury遍尝各种体育项目，
but never excelled at anything, until, at the age of 16, he turned to the high jump.
却始终没在哪一项出头，直到16岁那年，他试了跳高运动。
But when he couldn't compete against the strong athletes at his college using the standard high jump techniques of the time,
起初他仍然无法使用当时的标准式跳法击败学院中的无数优异选手
Fosbury tried to jump a different way: backwards.
Fosbury转而尝试与众不同的方法：背跃。
Instead of jumping with his face towards the bar, bringing each leg over in the traditional straddle method,
不像一般选手般面向杆子翻转，两脚依次翻过的剪刀式跳法，
he jumped with his back towards the bar.
Fosbury转而以背向越过横杆。
Fosbury improved his record by over half a foot,
如此使他的成绩跃进了超过半英尺，
and left his coaches amazed by this strange new style of high jumping.
也使教练目瞪口呆，折服在这诡异的新跳法面前。
During the next few years, Fosbury perfected his high jump style, won the U.S. National trials,
之后数年，Fosbury完善了他的背跃绝技，通过了美国的国手选拔，
and assured his place in the 1968 Olympics in Mexico.
并在1968年墨西哥城奥运会确立了他的历史定位。
In the Olympic Games, Fosbury amazed the world with his new technique,
在奥运会上，Fosbury以他的独门绝活惊艳了全世界，
winning a gold metal with an Olympic record leap of 2.24 meters.
并一举夺下金牌，还顺便将奥运会的记录由2.22米提高到了2.24米。
By the next Olympic Games, almost all of the competing of high jumpers had adopted what came to be known as the Fosbury Flop.
于是下一届奥运会中，几乎所有选手都转而使用了这一名为Fosbury鱼跃的跳法。
What's the secret behind the technique?
这个招式背后的秘密为何？
It lies in a physics concept called the center of mass.
答案藏在一个叫质量中心（质心）的物理概念里。
For every object, we can locate the average position of all of its mass by taking into account how the mass is spread around the object.
对任何物体，我们都可以通过考虑物体质量在三维空间中的分布情形来确定其质量的平均位置。
For instance, the center of mass of a flat, rectangular object of uniform density
例如，一个扁平、长方形、密度均一的物体，
will be in the intersection of both diagonals, in equal distance from each corner.
其质心会落在两对角线的交点，与四个角等距。
We can find the center of mass for other objects by similar calculations,
对于别的物体，我们可以透过类似的方法去寻找其质量中心，
or by finding the object's balancing point, which lies right underneath its center of mass.
或是直接找物体的平衡点，平衡点会落在质心的正下方。
Try balancing a broom by holding it and slowly bringing your hands together until they meet.
试试看，双手虎口托着扫把的柄，并轻轻用力让两手往内滑动，直到手掌合十。

This balancing point lies right underneath the broom's center of mass.
这时扫把的平衡点就会在质心的下方。
We humans also have a center of mass.
我们人类也有一个质心。
When most people stand up, their center of mass is around the belly,
大多数人站直时，质心位在肚脐附近，
but what happens to your center of mass when you lift your hands in the air?
但当你举起双手，你的质心会发生什么事？
Your center of mass moves upwards.
你的质心会向上移动。
It moves all the time as you move through the day, based on how your body is positioned.
在你一天的活动中，你的质心会根据你的姿势四处动来动去。
It can even move outside of your body.
甚至有些姿势会让你的质心在身体的外部。
When you bend forward, your center of mass is located below your bent belly in a place where there is no mass at all.
例如腰向前仰，质心会在你的腹部前（下）方，即使那一点空无一物。
Weird to think about, but that's the average position of all your mass.
想起来似乎怪怪的，但它确实是这时你身体所有部分的平均位置。
Many objects' center of mass are outside their bodies. Think of doughnuts or boomerangs.
还有许多物品的质心处在物品外面。想想甜甜圈和回飞镖吧。
Now look at the Fosbury Flop, and follow the position of the center of mass of the jumper.
现在我们能回来看Fosbury的后跃了，注意动作中运动员的质心位置。
The jumper runs very fast, so he can divert his horizontal velocity to vertical velocity, and jumps.
选手首先高速助跑，于是可通过最后的一蹬，将一部分的水平速度转移成垂直起跳的速度。
Wait for it ... there. Look at the jumper's center of mass as his body bends backward.
留神...就是这里。注意到选手身体往后弓起时质心所在的位置了吗？
It's below the bar. That is the secret behind the jump.
事实上它还在横杆之下。这就是背跃绝技的奥秘。
With the old, pre-Fosbury techniques,
在旧的、Fosbury以前的跳高技术中
the jumper had to apply enough force to lift his center of mass above the bar by a few inches in order to clear it.
跳高选手必须拼命使劲，以此将他们的质心抬到杆子以上数英寸，才能避免越过时把杆子撞掉。
The Fosbury Flopper doesn't have to do that.
但背跃式跳高回避了这个瓶颈。
The genius of the Fosbury Flop is that the jumper can apply the same amount of force,
背跃式跳高的天才之处在于，选手花同样力气，其质心和原来一样高，
but raise his body much higher than before.
身体却能处在更高位。
That means he can raise the bar so high that even when his center of mass can't go any higher, his arching body can.
这代表杆子能继续往上摆，即使质心的高度再也提升不了，弯曲的身体却可以由上方溜过去。
Fosbury's technique brought the high jump to new heights by splitting the jumper's body away from his center of mass,
Fosbury的新招式让跳高的世界纪录连创新高，原理是尽量弯曲身体，使选手的质心离身体越远越好，
giving it that much more room to clear higher and higher bars.
因此有更多空间能运用于闪过不断加高的横杆。
So the Fosbury Flop may be sports history's only great leap forward, that is also a great leap backward.
因此可以说，背跃式跳高是运动史上的一次向前大飞跃，而这实际上是向后飞跃。