Final answer:
Density is an important characteristic of substances and is crucial in determining if an object sinks or floats. It is the mass per unit volume of a substance and is affected by the distance between atoms and molecules.
Step-by-step explanation:
Density, as you will see, is an important characteristic of substances. It is crucial, for example, in determining whether an object sinks or floats in a fluid. Density is the mass per unit volume of a substance or object. Atoms and molecules are close together in solids and liquids, and in gases they are separated by empty space. Thus, gases have lower densities than liquids and solids. The density of a substance can also help identify its composition and reveal something about its phase and substructure.