Specific gravity is a particularly useful quantity with regard to buoyancy. For instance, the density of aluminum is 2.7 in g/cm3, but its specific gravity is 2.7, regardless of the unit of density. Specific gravity, being dimensionless, provides a ready comparison among materials without having to worry about the unit of density. Specific gravity=Density of material/Density of water Specific gravity is defined as the ratio of the density of the material to the density of water at 4.0☌ and one atmosphere of pressure, which is 1000kg/m 3: For this reason, a more convenient, dimensionless quantity called the specific gravity is often used to compare densities. A chunk of Swiss cheese is an example of a heterogeneous material containing both the solid cheese and gas-filled voids.ĭensity is a dimensional property therefore, when comparing the densities of two substances, the units must be taken into consideration. If the density of a substance were not constant, the substance is said to be a heterogeneous substance. The density is constant throughout, and the density of any sample of the substance is the same as its average density. A solid iron bar is an example of a homogeneous substance. If the density is constant throughout a substance, the substance is said to be a homogeneous substance. The density of a substance is not necessarily constant throughout the volume of a substance. The density of solids and liquids normally increases with decreasing temperature. The densities of the solids and liquids displayed are given for the standard temperature of 0.0 ° CĪnd the densities of solids and liquids depend on the temperature. The gases are displayed for a standard temperature of 0.0 ° CĪnd a standard pressure of 101.3 kPa, and there is a strong dependence of the densities on temperature and pressure. The densities of gases are much less than those of liquids and solids, because the atoms in gases are separated by large amounts of empty space. The densities of liquids and solids are roughly comparable, consistent with the fact that their atoms are in close contact. The density of an object may help identify its composition. The metric system was originally devised so that water would have a density of 1g/cm 3, equivalent to 10 3kg/m 3. Where p (rho) is the symbol for density, m is the mass, and V is the volume.