平衡我认为首先是水平方向。因为风是水平方向。
KITE一定有个仰角。风力在KITE上产生上升力的同时必有水平方向的分量。垂直方向有重力可以平衡上升力，水平方向没有线没法平衡。
线的弹簧作用不在于位移，而在于其力的变化。这对稳定是关键。

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送交者: gyro 于 2009-11-03, 17:08:04:

回答: GYRO,这问题有点意思。 由 JFF 于 2009-11-03, 13:10:24:

Without the line the kite will move upward and far away. But the motion must be unstable to tilting and rotation.
With the line the kite is in equilibrium and stable. The elasticity of the line is not essential.

I am just stating the obvious. You must be thinking about something else.