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※ 引述《Rivendell (Rivendell)》之銘言：
: ※ 引述《Rivendell (Rivendell)》之銘言：
: :   如題
: :   到底會不會啊？
: :   我想確定一下...
:   suppose you havetwo infinite straight line charge x ,a distance d apart,
:   moving along at aconstant speed v. how great would v have to be in order
:   for the magnetic attraction to balance the electrical repulsion?
:   解答最後算出速度要等於光速
:   這題是怎麼回事啊？
在兩線靜止坐標上（速度＝0）的觀察者只看到靜電排撤。
其它坐標必需也觀察到排撤。
如果在某速度兩力平衡，那超越這速度就會兩線相吸，不符合相對原則。
所以這速度必需是不可超越的限速：光速

--
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Your life is valuable for its own sake.
You are not second-class in the universe, deriving meaning and purpose from some other mind.
You are not inherently evil—you are inherently human, possessing the positive rational potential to help make this a world of morality, peace and joy.
Trust yourself.


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