what does density do
1 The density of a substance is the relationship between the mass of the substance and how much space it takes up (volume). 2  The mass of atoms, their size, and how they are arranged determine the density of a substance. 3  Density equals the mass of the substance divided by its volume; D = m/v.he density of an object is the mass of the object compared to its volume. The equation for density is: Density = mass/volume or D = m/v. Each substance has its own characteristic density because of the size, mass, and arrangement of its atoms or molecules.