密度是物质的基本性质,每种物质都有自己的密度.密度知识在生活中有广泛的应用.例如,利用密度知识可以鉴别金戒指是不是纯金的,勘探队员在野外勘探时,通过对样品密度等信息的采集,可以确定矿藏的种类及其经济价值,在农业生产中利用盐水可以选种等,都是利用了不同物质的密度一般不同这一特点.那么是不是所有物体的密度都是一成不变的呢?学习密度知识,除了要理解密度是物质的性质之外,还需要知道密度的双重性:不变性与可变性. Density is the basic nature of the material, each material has its own density. Density knowledge in life has a wide range of applications.For example, the use of density can be identified gold ring is not gold, exploration team exploration in the wild, by Sample density and other information collection, you can determine the type of mineral resources and their economic value, the use of salt water in the agricultural production can be selected, are based on the use of different materials, the density of the general characteristics of this is not the density of all objects Is immutable? Learning density knowledge, in addition to understanding the density of the nature of the material, but also need to know the duality of density: invariance and variability.