Density (r) of a material is defined as mass per unit volume
and is usually represented in the SI system by the units g*cm-3 or kg*m-3.
There are a number of different methods and devices for determining the density of a
substance, and there are also a number of factors that can affect the density of a sample.
If the exact composition of a non-homogeneous material is known, its solid density (rs) can be determined using the mass and density of each
of the n components using the following equation:
The density of materials such as agricultural grains, which consist of many small
particles, can be expressed in terms of solid density, particle density or bulk density.
Solid density considers the mass and volume of the solid matter only and does not include
any air spaces within the mixture. Particle density describes the mass per unit volume of
an individual particle (e.g. corn kernel) from the sample. Bulk density, on the other
hand, considers the total mass and total volume of a large quantity of the particles.
Specific gravity is a dimensionless term used to compare the densities of different materials relative to water. Specific gravity of a substance is defined as the ratio of the substance’s density to the density of water at the same temperature. From this information, it can be determined that if the specific gravity of a material is less than 1, it is less dense than water, and if the specific gravity is greater than 1, it is more dense than water.
1. Stroshine and Hamann. 1994. Physical Properties of Agricultural Materials and Food Products. 17-18.