一秒转4圈半！羽生结弦挑战的4A到底有多难？3分钟英文短片告诉你！（附视频&解说稿）
2月10日上午，北京冬奥会花样滑冰男子单人滑自由滑项目的比赛在北京首都体育馆进行。曾蝉联过去两届冬奥会该项目的冠军羽生结弦，挑战了花滑届的最高难度4A动作。
但遗憾，前2个动作都摔倒在了冰面上。最终获得188.06分，总分283.21。
花样滑冰（figure skating）兼具美感和动感，有着“冰上芭蕾”的美称，运动员在冰面上要完成跳跃、旋转等一系列动作。
对于普通人来说，转一圈或者两圈都会很晕。为什么花滑运动员不仅能在冰面上完成跳跃、多次旋转等高难度动作？而且还不会转晕？这个被认为是挑战人类极限的动作，到底有多难？3分钟英文短片告诉你一个科学的答案。
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This is the hardest jump in figure skating.
Four complete revolutions in the air.
It's called a quadruple jump.
And it's changing the sport of figure skating.
Today's figure skaters are more focused on jumps than ever before.
That's led to incredible displays of athleticism, but not everyone is happy about it.
For lots of fans, quadruple jumps have done little but make figure skating uglier and more dangerous.
And they may be right.
A quadruple jump is extremely difficult.
The leap requires incredible momentum, precisely divided between vertical lift and spin.
Then you have to fight inertia to contract your body, making yourself spin faster.
Finally, you land with a force equivalent to seven times your body weight.
And all of this on a surface where many people struggle to stand up.
It all takes less than a second.
American figure skater Nathan Chen does five of these jumps in his long program.
Now, all quads aren't created equal.
First, there's the Lutz, where you take off from the back outside edge of your left skate and land on your right foot.
What makes it so hard is that you reverse direction on takeoff.
Your left foot is skating clockwise, but then you jump and spin the other way.
Then there’s the flip jump, which launches from the left foot, and the toe loop, which launches from the right.
And finally there's this one, called the Salchow.
It was invented more than a hundred years ago by the first Olympic figure skating champion.
These jumps are pushing the limits of figure skating.
But they're also fundamentally changing the sport.
Most quads—or passes where a skater does a quad and then another jump— get negative grades of execution.
Meaning, they're sloppy.
Half of those are total disasters.
And even Chen makes mistakes on about one-third of his quad passes.
That means nearly everyone falls, and as athletes take more risks, many get injured.
But those injuries haven’t stopped other skaters from trying to push their routines even further.
Some skaters are even trying to pull off a quadruple axel, a forward-facing leap with four and a half rotations.
That would change the sport all over again.
But it also raises a question: If figure skating has turned into a quest for bigger and bigger jumps, can it still be about artistry?
4A又叫阿克塞尔四周跳。阿克塞尔跳是花样滑冰六种跳跃动作中的一种，又称前外点冰跳，由挪威选手阿克塞尔·保尔森在1882年首次完成，是男单6种跳跃中最难的动作。
Figure skating is known for its dashing moves. There is one called the "quad Axel," or "4A," that is widely considered to be the hardest jump in figure skating.
The Axel, also known as the Axel Paulsen jump after its creator, is the most difficult one. It is a type of "edge jump," meaning skaters have to skate on one side of the blade when lifting off the ice.
4A之所以如此难，是因为4A虽然被算作四周跳，但要多半周，实际要转四周半。
与3A相比较，4A的最高点要高了足足17cm，落冰点距离要远了1.1m，为了实现这些成功条件，助滑速度需要提高10%，再加上A跳是唯一一个向前的跳跃，在准备进入转体的时候重心在冰刀的外刃上，在起跳时，冰刀可能会横向打滑，所以让这个跳跃动作成了世界上难度最大的动作。
理解了这个概念之后呢，我们再来做一下技术分析啊，完成这个动作呢，选手只有0.7秒的时间，但是要转上1620度，选手在空中旋转的速度达到了每秒钟6圈半，相当于一辆每小时50公里的小汽车的车轮的转速啊！速度这么快，落冰的时候啊，冲击力是体重的5倍！如果选手的体重是120斤的话，也就是说对地面的冲击力同时也是选手自身受到的冲击力会达到600斤。
此外，A跳是一个向前跳跃的动作，在转体之前，运动员的重心不可避免地处于冰刀的外侧，如果稍不注意，冰刀极有可能发生横向打滑，危险性很大。
羽生结弦在北京冬奥会选拔赛的赛前公开训练赛上，曾首次成功完成4A，但也难以轻松驾驭。在备战北京冬奥会的训练中，他尝试了几次4A，但也没有成功。自由滑中冲击4A，第一跳羽生结弦出现了失误，摔倒在地。
作为花样滑冰中难度最大的一个跳跃动作，此前从未有运动员在正式比赛中完成过4A，但羽生将做到4A视作了自己的使命。
虽然此次在北京冬奥会男子自由滑比赛中做“4A”动作时摔倒，但在本场比赛的赛后裁判打分表上，羽生结弦的动作被认定为“4A”动作。这也是“4A”动作这个动作第一次出现在了冬奥会的裁判打分表上。
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