The present quality used to be called weight, but in order to unify international standards, it was changed to quality. Generally speaking, how heavy this object is, the concept of weight will be equated with quality, but it is a representation of quality in words.

3. The international unit of mass is kilogram (symbol Kg), and other commonly used units are tons, grams, milligrams, etc. Balance is a common tool for measuring quality in the laboratory.

4. The mass of the same object is usually a constant and does not change with height or latitude. But according to Einstein's theory of relativity, the mass of the same object will change with the change of speed.