他给玩具车上发条然后松手让它跑。
先把刀握紧不要松动，然后端起肩膀，让手臂从你头的上方开始挥动，并在胳膊指向目标的那一瞬间松手。
Envision the knife sticking. Then, with your shoulders square, start above your head and release with your arm extended toward the target.
然后我松手，当我把力撤销，这个弹簧最后的长度,比它一开始要长。
And then when I relaxed, when I took my force off, the spring was longer at the ends than it was at the beginning.
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