关于球体，法向量是,除以球的半径。

So, for a sphere, the normal vector is divided by the radius of the sphere.

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在球运行路径的某一点(10米处，或人墙的位置)球的速度下降，使空气在球体表面形成较稳定的层流。

Some way into its path - perhaps around the 10 m mark (or at about the position of the wall of defenders) - the ball's velocity dropped such that it entered the laminar flow regime.

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开始动作如图所示：两臂伸直，背部保持平直，两腿充分蹬伸，脚掌置于健身球的球体之上。

Start as shown with the arms extended, back flat, legs fully extended and the balls of the feet on the Swiss ball.

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