来自《耶鲁大学开放课程：生物医学工程探索 第19集 第19集》
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although that would be easier in a sense,尽管这样从某种角度看要容易些 -
because if your feet are both on the ground因为如果你的双脚一直在地上 -
balance is not so hard.就不难保持平衡了 -
Once you lift a foot off the ground一旦你把一只脚抬离地面 -
the other problem it introduces is balance.就引入了另一个问题 也就是平衡问题 -
It's much harder for me to stay stationary on one leg than用一只脚保持静止 -
it is on two legs比用双脚保持静止难得多 -
because gravity is acting on my body因为重力作用在我身上 -
and trying to pull me back down again.并把我往下拉 -
An additional problem arises这样一个额外问题出现了 -
with this lifting up of one foot它与一只脚抬起来有关 -
and that is the problem of balance.这就是平衡的问题