How Is Density Calculated?
The Concept
Density is a measure of the how much of something exists within a specific space or period of time. We use the concept of density to describe population overload and other social and psychological concepts when we look at cultural factors for such effects as stress. In the physical sciences, density is used to describe vegetation (geography), rock type (geology) or solar systems (astronomy). The most common type of density that scientists use is the hardest for most non-scientists to understand; the density of basic forms of matter called molecules. In chemistry and physics, density is computed by dividing the mass of an object by the volume of space it occupies. Physicists and chemists use density to describe elements and compounds, to understand chemical and nuclear reactions and to verify results. Archimedes is said to have developed the theory of buoyancy while attempting to verify whether the gold in a wreath was pure or false by finding its density.
The Formula
Calculate the density of a solid or liquid by dividing the mass (or weight) of the object by the volume it fills. Density is stated in mass per unit of measure. The international scientific (SI) measure for density is kilograms (kg) per cubic meter (m). For example; if 1000 cubic centimeters of cork weigh .240 kg, we could find that the density of cork is .240 kg per 1000 cubic centimeters or 240 kg/cubic meter (SI). Liquid density is given in kg per liter (L) or grams (g) per cubic milliliter (ml) or cubic centimeter (cm). Water, which weighs 1000 kg per cubic meter, is used as the standard (one cubic meter equals 1000 liters, so the density of pure water at 4 degrees Celsius and sea level is one kg/L). The density of gas is a bit more complex: its density is computed by dividing the product of the molar mass (the weight of a mole of the gas, available on periodic tables of the elements) and pressure by the product of the Universal gas constant (8.314472, a number determined by experimentation) and temperature in degrees Kelvin. Although density is sometimes expressed using U.S. or Imperial units in the social sciences, the metric system is the standard for physical scientists and a majority of the countries in the world, giving rise to numerous conversion machines on the internet.
Variables
Density is not absolute. It is affected by gravity and atmospheric conditions. Allowances must be made for elevation, temperature and humidity because these conditions affect the way molecules move. Cold, for example, increases the density of frozen water. At higher altitudes, water boils at a lower temperature, its density decreasing due to lower air pressure and gravitational pull. Chemical reactions can alter the density of a substance, too. Although the density of water would not be changed by a suspension of another substance like petroleum, it would change if chlorine were added to make hydrochloric acid.
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