because it's a unit disk. And, the center of mass is the center of a disk.
因为它是一个单位圆盘，这部分的中心就是圆盘的中心。
Cattle produced the least carbon dioxide per unit of body mass.
每单位体重，牛产生的二氧化碳最少。
A unit of measurement for mass.
用于测量质量的单位。
Mass per unit of volume in powder form, including the air trapped between the particles.
每单位体积粉末的质量，包括粒子之间的空气。
In physics it is an identification of material by noting its mass per unit volume.
在物理学上，是以每单位体积的质量来鉴别物质。
ASTM D5848 Standard Test Method for Mass Per Unit Area of Pile Yarn Floor Coverings.
ASTMD5848簇绒纱线地毯单位面积质量的试验方法。
The plate unit could better simulate the occurrence of rock mass;
使用板状结构单元可以很好地模拟岩体产状；
The plate unit could better simulate the occurrence of rock mass;
使用板状结构单元可以很好地模拟岩体产状；
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