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。
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。
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。
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