来自《耶鲁大学开放课程：基础物理 第15集 第15集》
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How about somebody riding with the particle?如果有人与质点同行呢 -
If you're riding with the particle如果你与质点同行 -
your 0 component你的 0 分量为 -
is m0·c, is m·c.m0·c 就是 m·c -
There is no velocity for you, and you have no momentum,而质点相对于你速度为零 动量也为零 -
as the particle has no momentum as seen by the particle,就像从质点角度看质点也不具有动量 -
so the components of the vector P所以矢量 P 的分量 -
become m·c and 0.变成了 m·c 和 0 -
What's the length square of this vector?这个矢量的模的平方是多少 -
Well, it's the square of this guy and case closed;这是这个值的平方 算完了 -
there's nothing here to subtract from here.这里不用再减去什么 -
That's a quick way to verify这也快速地证明了