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一切量值总是表达为一个数与一个单位之积。有一些无量纲量,它们只用纯数表达。例如:相对分子质量;质量分数;化学计量数;相对密度。实际上,他们的单位是“1”,因而在表面上反映不出来与一个单位相乘了。对于一切无量纲量的量值,由于在任何单位制中它们的单位都是“1”,而不存在计量单位变化的计算问题,本文只涉及那些有量纲的量值。以不同的单位,可以表达同一个量值,例如:对于大气压力,既可以用标准大气压 atm 作为单位表达,也可以用帕斯卡表达,只是单位前的数值随单位的变化而比例地变化。1.单位变化的基本原则与方法单位变化不应带来原量值的变化。因此,为了改变单位而乘到原量值上的因子恒
All values are always expressed as a product of a number and a unit. There are some dimensionless quantities, they are expressed in pure numbers only. For example: relative molecular mass; mass fraction; stoichiometry; relative density. In fact, their unit is “1”, so it does not appear superficially multiplied by a unit. For all dimensionless quantities, since there are “1” units in any system of units and there is no calculation of the change in units of measure, this article deals only with those with dimensions. In different units, the same value can be expressed. For example, atmospheric pressure can be expressed in terms of atm as a unit of atmospheric pressure or Pascal, except that the value before the unit varies proportionally with the unit. 1. Unit changes in the basic principles and methods Unit changes should not bring changes in the original value. Therefore, the factor multiplied by the original value in order to change units is constant