来自《耶鲁大学开放课程：基础物理 第7集 第7集》
-
"How fast should I fire a gun"射出时的速度要多大 -
so the bullet never comes back?"子弹才不会回来" -
Well, you should fire it so that it can go to infinity.那就得让它能达到无穷远 -
When it goes to infinity,当它到达无穷远的点 -
you want to just manage to get there;你想要它刚好仅仅能够到达那里 -
it's going to go to infinity, stagger, and fall down.它会在无穷远处摇摆不定 然后落下 -
Well, it's got no kinetic energy in infinity,它在无穷远点得不到动能 -
it's got no potential energy in infinity.在无穷远处 势能也为零 -
Therefore, its total energy should be 0.因此总能量应该为零 -
Therefore, what you should do--所以你要做的是 -
At the surface of the Earth在地球表面 -
your (1/2)·m·v^2 - G·M·m / RE should be 0,你的 (1/2)·m·v^2 - G·M·m / RE 应该是零