Though an ion engine could never lift a spacecraft out of Earth's gravity well.
尽管离子发动机不能使航天飞机很好地摆脱地球引力。
Well, that is the difference between the equation with gravity and without gravity.
该差值即是存在重力,与不存在重力方程的解之差。
Mg Well, we have here a force Mg; that's gravity.
这个力为，它是重力。
Well, the general equations, now, which deal in gravity...
现在一般性方程引入，到了重力的例子里。
And you will say, "Well, gravity is in this direction."
你会告诉我，是这个方向。
And you will say, "Well, gravity is in this direction."
你会告诉我，是这个方向。
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