Kepler's second law means that a planet's orbital speed changes with its distance from the sun.
开普勒第二定律指行星的轨道速度与其和太阳的距离。
Well, that's completely trivial, you would say, because it is one-half * of the mass of the Earth times the orbital speed squared.
也许你会说，这是，完全没有意义的,它等于1/2m地,轨道速度的平方。
But now notice, I can substitute now for this v squared, I can substitute the square of this that is the orbital speed and then I get M G over R.
现在注意我能,代替这个v平方，我能代入这个平方,那是轨道速度,然后得到MG在R上。
It is not as much a coincidence as you think, of course. But if something is in orbit, this is the orbital speed at radius r, then always is its total energy is half the potential energy.
但并不是巧合，当然，但如果某物在轨道里，这是在半径r的速度，则总是它的总能量，是势能的一半。
If you want to escape from this, you will need a speed which is the square root of two times larger than that orbital velocity.
如果想要逃离这里，你将需要一个速度，是轨道速度2倍大的，平方根。
The 15 minute sub-orbital flight achieved an altitude of 116 miles and a maximum speed of 5, 134 miles per hour.
这次15分钟的亚轨道飞行达到了海拔116英里的高度，最大速度为每小时5134英里。
The 15 minute sub-orbital flight achieved an altitude of 116 miles and a maximum speed of 5, 134 miles per hour.
这次15分钟的亚轨道飞行达到了海拔116英里的高度，最大速度为每小时5134英里。
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