Density is a physical property of matter as each element and compound has a unique density associated with it.It is also defined as a qualitative quantity of the measurement of the relative heaviness of objects with a constant volume.In layman's term, it is closely "packed" or "crowded" the material appears to be.Density as a quantity, cannot be directly perceived or measured.It is calculated by the formula
ρ (the lower case Greek letter rho) where ρ is the density,
m is the mass, and
V is the volume. In some cases (for instance, in the United States oil and gas industry), density is also defined as its
weight per unit volume,
although this quantity is more properly called
specific weight.
Density of a regularly shaped object can be calculated easily having the volume and mass. On the other hand, density of irregularly shaped objects like stone are to calculated if the volume is already available.In getting the volume, the Archimedes Principle is applied, or simply the displacement method. With water and a container, volume is at reached.(Figure 2)
Figure 2
Less dense fluids float on more dense fluids if they do not mix. This
concept can be extended, with some care, to less dense solids floating
on more dense fluids. If the average density (including any air below
the waterline) of an object is less than water it will float in water
and if it is more than water's it will sink in water.
In some cases density is expressed as the
dimensionless quantities specific gravity or relative density,
in which case it is expressed in multiples of the density of some other
standard material, usually water or air/gas. (For example, a specific
gravity less than one means that the substance floats in water.)
The mass density of a material varies with temperature and pressure.
(The variance is typically small for solids and liquids and much greater
for gasses.) Increasing the pressure on an object decreases the volume
of the object and therefore increase its density. Increasing the
temperature of a substance (with some exceptions) decreases its density
by increasing the volume of that substance. In most materials, heating
the bottom of a fluid results in
convection
of the heat from bottom to top of the fluid due to the decrease of the
density of the heated fluid. This causes it to rise relative to more
dense unheated material
.
The reciprocal of the density of a substance is called its specific volume, a representation commonly used in
thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass.
