Density is the number of things—which could be people, animals, plants, or objects—in a certain area. To calculate
density
, you divide the number of objects by the measurement of the area.
The population density of a country is the number of people in that
country
divided by the area in square kilometers or miles. The
country
of Singapore is one of the most densely populated countries in the world. It has a population of 4,839,400 and an area of 687 square kilometers (265 square miles), so its
density
is 7,044 people per square kilometer (18,262 per square mile).
Of course, not all the people in the
country
are spread out evenly. Cities have a greater
population
density
than rural areas.
Density
can also be used to refer to the number of plants or animals in a certain area. Sometimes, animal or plant populations are too dense. This leads to overpopulation.
Deer have overpopulated areas of the Midwestern United States, for example. A common reason is a lower
density
of their natural predators, such as pumas or bears. As a result of the
deer
’s dense population, the competition for land and food is heightened and many
deer
die of starvation. Vegetation does not have time to develop, so food becomes scarce. A habitat can only support a limited number of each type of organism, so an
overpopulation
of
deer
can drive those
deer
to other
habitats
, including human
habitats
such as towns.
Density
can refer to the number of molecules in a substance. This can apply to gases, liquids, and solids.
Air quality is defined by the number of pollutants in a certain area.
Air quality
therefore measures the
density
of air
pollutants
, such as smoke and emissions. Densely populated cities often have poor
air quality
because of the air pollution
density
.
Density
is used to measure the salinity of seawater. Water densely packed with salt has a high
salinity
. Water that has few salt
molecules
has low
salinity
.
Rocks and minerals are also measured for
density
. Many igneous rocks, or
rocks
formed from volcanic eruptions, have a low
density
. They are full of pockets of air. One type of
igneous
rock
, pumice, has such a low
density
that it can actually float on water. The water is more dense than the
rock
.
Fast Fact
Elbow Room in Africa
Namibia, one of the least densely populated countries in the world, has just 2.6 people per square kilometer (6.6 per square mile.)
