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A raised weight can produce work, but in doing so it must necessarily sink from its height, and, when it has fallen as deep as it can fall, its gravity remains as before, but it can no longer do work.
一个增加的重量可以产生功，但是在这样做的时候，它必须从它的高度下降，当它下降到它所能下降的最大深度时，它的重力仍然和以前一样，但是它不能再做功了。