Mass, Volume, and Density

A sponge is an example of a substance with a low density

Density is a physical property that is unique to all substances. It is a measure of a substance’s mass compared to its volume. The greater the mass per unit volume for a substance, the greater its density will be. A substance with a large density value has its particles packed very closely together, like lead. A substance with a low value for density will have its particles packed very far apart. A sponge or a marshmallow is an example of a substance with low density. Very specifically, if the density of an object is less than one gram per milliliter it will actually float in pure water, which has a density of exactly one gram per milliliter. Objects with a density greater than one gram per milliliter will sink in pure water. Density is a very important property to study.  In fact, small differences in the density of saltwater compared to pure water are one of the most important processes that control the worldwide motion of the ocean.