To calculate the density (usually represented by the Greek letter "rho") of an object, take the mass (m) and divide by the volume (v):
rho = m / vThe SI unit of density is kilogram per cubic meter (kg/m3). It is also frequently represented in the cgs unit of grams per cubic centimeter (g/cm3).
Using DensityOne of the most common uses of density is in how different materials interact when mixed together. Wood floats in water because it has a lower density, while an anchor sinks because the metal has a higher density. Helium balloons float because the density of the helium is lower than the density of the air.
When your automotive service station tests the antifreeze, they will pour some into a hydrometer. The hydrometer has several calibrated objects, some of which float in the liquid. By observing which of the objects float, it can be determined what the density of the liquid is ... and, in the case of antifreeze, if the chemicals are still strong enough to retain the necessary freezing point.
Another important consequence of density is that it allows you to solve for mass and volume, if given the other quantity. Since the density of common substances is known, this calculation is fairly straightforward, in the form:
v * rho = m
m / rho = v
The change in density can also be useful in analyzing some situations, such as whenever a chemical conversion is taking place and energy is being released. The charge in a storage battery, for example, is an acidic solution. As the battery discharges electricity, the acid combines with lead in the battery to form a new chemical, which results in a decrease in the density of the solution. This density can be measured to determine the battery's level of remaining charge.
Density is a key concept in analyzing how materials interact in fluid mechanics, weather, geology, material sciences, engineering, and other fields of physics.