An athlete uses physics to shatter world records - Asaf Bar-Yosef

一位用物理征服世界紀錄的運動員 - Asaf Bar-Yosef

譯者: 紀維 秦 審譯者: Geoff Chen

In the early 1960s,

1960 年代初

Dick Fosbury tried his hand at almost every sport,

Dick Fosbury 幾乎遍嘗各種體育項目，

but never excelled at anything,

卻始終沒在哪一項出類拔萃。

until, at the age of 16, he turned to the high jump.

直到 16 歲那年，他相中了跳高運動。

But when he couldn't compete against

起初他仍然無法擊敗

the strong athletes at his college

學院中的無數優異選手

using the standard high jump techniques of the time,

－－使用當時的標準式跳法，

Fosbury tried to jump a different way: backwards.

Fosbury 轉而嘗試與眾不同的方法：背躍。

不像一般選手般面向桿子翻轉

Instead of jumping with his face towards the bar,

bringing each leg over in the

兩腳依次翻過

的剪刀式（straddle）跳法，

traditional straddle method,

he jumped with his back towards the bar.

Fosbury 轉而以背向越過橫桿。

Fosbury improved his record by over half a foot,

如此使他的成績躍進了 15.24 公分，

and left his coaches amazed

也使教練目瞪口呆，

by this strange new style of high jumping.

折服在這詭異的新跳法面前。

During the next few years,

往後數年，

Fosbury perfected his high jump style,

Fosbury 完成了他的背躍絕技，

won the U.S. National trials,

通過了美國的國手選拔，

and assured his place in the 1968 Olympics in Mexico.

並在 1968 年墨西哥城奧運會 掙得了他的歷史定位。

In the Olympic Games, Fosbury amazed the world

在奧運會上，Fosbury 驚艷了全世界

with his new technique, winning a gold metal

並以他的獨門絕活一舉奪下金牌，

with an Olympic record leap of 2.24 meters.

還順便推進了奧會記錄，由 2.22 到 2.24 公尺。

By the next Olympic Games,

於是下一屆奧運會中

almost all of the competing of high jumpers

幾乎所有選手都轉而使用了

had adopted what came to be known as

新的背躍式跳法，或者 其傳世名號：Fosbury 的魚躍。

the Fosbury Flop.

（flop 有重摔、失敗之意，為一個制勝絕技取這個不相稱名字的是一名記者，認為以彎曲的背部墜落軟墊，像上岸的魚亂跳 ）

What's the secret behind the technique?

這個招式背後的祕密為何？

It lies in a physics concept

答案藏在一個物理概念裡：

called the center of mass.

稱為質量中心（質心）。

For every object,

對任何物體

we can locate the average position of all of its mass

我們都可以藉由

考慮物體質量 在三維空間中的分佈情形

by taking into account how the mass

is spread around the object.

來確定其質量的平均位置。

For instance, the center of mass

例如，一個扁平、長方形、

of a flat, rectangular object of uniform density

密度均一的物體，其質心

會落在兩對角線的交點，

will be in the intersection of both diagonals,

in equal distance from each corner.

與四個角落等距。

We can find the center of mass for other objects

對於別的物體 我們可以透過類似的方法

by similar calculations,

去尋找其質量中心。

or by finding the object's balancing point,

或是直接找物體的平衡點，

which lies right underneath its center of mass.

平衡點會落在質心的正下方。

Try balancing a broom by holding it

試試看，雙手虎口托著掃把的柄，

and slowly bringing your hands together until they meet.

並輕輕用力讓兩手往內滑動，直到手掌合十。

This balancing point lies right underneath

這時掃把應該還是平衡的， （試著想想看原理為何）

the broom's center of mass.

掃把的質心就在兩手正中上方某處。

We humans also have a center of mass.

講到人類，人體自然也有一個質心。

When most people stand up,

大多數人站直時，

their center of mass is around the belly,

質心位在肚臍附近。

but what happens to your center of mass

當你舉起雙手，你的

when you lift your hands in the air?

質心會發生什麼事？

Your center of mass moves upwards.

質心會向上移動。

It moves all the time as you move through the day,

在你一天的活動中，你的質心據你的姿勢

based on how your body is positioned.

四處動來動去。

It can even move outside of your body.

甚至有些姿勢，會讓 你的質心位在身體的外部。

When you bend forward, your center of mass

例如腰向前仰

is located below your bent belly

質心會在你的腹部前（下）方，

in a place where there is no mass at all.

即使那一點空無一物。

Weird to think about, but that's the average position

想起來似乎怪怪的，但它確實是這時

你身體所有部分的平均位置。

of all your mass.

Many objects' center of mass

還有許多物品的質心

are outside their bodies.

處在物品外面，

Think of doughnuts or boomerangs.

例子有甜甜圈，和回飛鏢。

Now look at the Fosbury Flop, and follow the position

現在我們能回來看 Fosbury 的後躍了，

注意動作中運動員的質心位置。

of the center of mass of the jumper.

The jumper runs very fast,

選手首先高速助跑，於是

so he can divert his horizontal velocity

可藉由最後的一蹬，將一部分的水平速度

to vertical velocity, and jumps.

轉移成垂直起跳的速度。

Wait for it...there.

留神......就是這裡。

Look at the jumper's center of mass

注意到選手身體往後弓起時

as his body bends backward.

質心所在位置嗎？

It's below the bar.

事實上它還在橫桿之下！

That is the secret behind the jump.

這就是背躍絕技的奧秘。

With the old, pre-Fosbury techniques,

在 Fosbury 登場以前，跳高的技術

the jumper had to apply enough force

全仰賴選手拼命使勁

to lift his center of mass above the bar

為了將他們的質心抬到桿子以上數吋

by a few inches in order to clear it.

才能避免越過時把桿子撞掉。

The Fosbury Flopper doesn't have to do that.

但背躍式跳法迴避了這個瓶頸。

The genius of the Fosbury Flop is that the jumper

Fosbury 方法的天才之處在於，

can apply the same amount of force,

選手花同樣力氣，其質心和原本一樣高，

but raise his body much higher than before.

身體卻能處在更高位。

That means he can raise the bar so high

這代表桿子能繼續往上擺，

that even when his center of mass

即使質心的高度再也提升不了

can't go any higher, his arching body can.

彎曲的身體卻可以由上方溜過去。

Fosbury's technique brought

Fosbury 的新招式讓跳高的

the high jump to new heights

世界紀錄連創新高，

原理是盡量彎曲身體，

by splitting the jumper's body

away from his center of mass,

使選手的質心離身體越遠越好，

giving it that much more room

因此有更多空間能運用於

to clear higher and higher bars.

閃過不斷加高的橫桿。

So the Fosbury Flop may be sports history's

因此可以說，Fosbury 絕技是運動史上

only great leap forward,

的一次向前大飛躍，

that is also a great leap backward.

藉由......向後飛躍。