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发表于 2012-4-20 04:14:34
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“适者生存”的进化论有道理。曾经解释过为什么鱼肚子是白的,而鱼背是黑的:
Generally speaking, fish's back skin receives direct sunlight from above whereas fish's stomach receives indirect sunlight either reflected from the bottom of the river/lake or scattered from the particles suspended in the water below the fish. In either case, the fish receives much more visible sunlight on its back skin than its stomach skin. In the process of evolution, fish likes to hide itself for survival. As a result, the stomach skin that receives much less visible sunlight will have much greater reflectivity than the back skin so that the reflected sunlight as a whole will give one very little information or contrast that there is a fish at that location. This is why fish's stomach is white.
重力的等位势面是水平面。在等位势面上通过垂直向扁型鱼身的左右摆动自由地改变速度和方向要方便一些吧。 |
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