and that means they've figured out

也就是说他们找到了
how to do this motion with their body

如何使自己的身体用最高效的方式
in the most efficient way.

完成这种运动的方法
Now, why would longer legs make it more efficient to move faster?

为什么腿长的人快速行走时效率更高
Well, because when you swing your leg you get a bigger bang for the buck,

因为在你动腿时腿长的人更合算
you get farther with one stride, that's part of it.

你一步能走得更远这是其一
The other part is that your leg, when it's in this swing motion,

还有就是你的腿在摆动运动中
behaves like another object

它与某种东西的动作很相似
you probably studied in physics, the pendulum.

你们可能在物理课学过那就是钟摆
You've seen pendulum's that swing,

你们见过来回摆的钟摆吧
you notice that the timing of pendulum's

你会发现钟摆的摆动周期是固定的
-anybody have a metronome?

有人有节拍器么