The basic concept of quantity

① Definition: A property that can be qualitatively distinguished and quantitatively determined by a phenomenon, object or substance. Understanding: a. According to the definition, the object to be studied can be a natural phenomenon or the substance itself. b. It should be noted that the two-fold meaning of this overview: it can be a generalized quantity or a specific quantity. On the one hand, the specific meaning of a quantity as commonly understood refers to a large definition: a property that can be qualitatively distinguished and quantitatively determined by a phenomenon, object or substance . Understanding: a. It can be seen from the definition that the object being studied can be a natural phenomenon or the substance itself. b. It should be noted that the two-fold meaning of this overview: it can be a generalized quantity or a specific quantity. On the one hand, the specific meaning of a quantity as commonly understood refers to concepts such as size, weight, length, etc.; on the other hand, the broad meaning of quantity refers to phenomena, The qualitative difference of objects or substances can be distinguished into quantities such as length, mass, time, temperature, hardness, current, and resistance. c. The quantity that can be compared with each other (comparable quantity) is called the same quantity. Some quantities of the same kind can be combined to form the same kind of quantities, such as: work, heat, energy; thickness, length, wavelength, etc. Generally speaking, any quantity can be measured. ②The quantity is expressed by a combination of a numerical value and a unit of measurement. It is meaningless to express the size of a quantity as a pure numerical value without a unit of measurement. ③Basic characteristics of the quantity: In general, the size of the quantity does not change with the measurement unit used, that is, only the unit and the value are changed. This is the basis for the interchange of various unit systems