# What is density?

What is density and what role does it play inhuman economic activity? To answer this question, let's look around. What do you see? A table, a computer chair, a table lamp, a plate with a sandwich. All these are solid bodies, then. to which you can touch, taste (even if you do not like the taste). Still there are liquids - water in the tap, milk in the package in the refrigerator, mercury in the thermometer, blood in the veins. There are also gases. The most banal example is the air breathed by the population of the planet Earth. There is neon, which glows in the signs, helium, which inflates balloons. All this can be called one word - substances.

Each substance has certain physical properties: heat capacity, electrical conductivity, density. Now we will consider what is the density.

## The tightness of any substance

The most well-known density formula is p = m / V, where p -volume, m - mass, V - volume of the studied substance. As can be seen from the dependence of density on mass and volume, when they change, the density of matter will also change. It directly depends on the mass of atoms, of which matter is composed. Thus, if atoms have a high mass, then the substance will have a greater density. However, if the substance has several different aggregate states, then the density in them will be completely different. Thus, the concepts of mass and density are absolutely interdependent.

## Units and types of density

Density is measured in kg / m³, and in the systemSI in g / cm³. If we consider porous and loose bodies, we can distinguish the apparent density, which is obtained by the ratio of mass to volume and the true density, which will be subtracted without taking into account the huge number of voids. The density depends directly on the ambient temperature. With decreasing temperature, density increases most often, but there are exceptions. For example, bronze, water and cast iron shrink when the temperature falls and become less dense.

To measure the density, you must use one of the following instruments: hydrometer, pycnometer or Zaidelman's drill.

## Density of urban population

Now let's consider what is the densityof the population. First of all, this is the number of inhabitants who live on one square kilometer of the area. The density of the population is distributed unevenly throughout the entire planet. This has a significant impact on the climate, the availability of fresh water and a huge number of other factors. In Russia, the average population density is 8.4 people / km², and in the world - 45 people per 1 sq. M. Every year, this figure is growing due to the natural increase in the population.

Calculate population density for a specificIf the area and number of inhabitants are known, it is very simple. You need to divide the number of inhabitants into the area of the territory and then you can get density. To know the density of the population is extremely necessary when calculating various economic factors and making forecasts.

Thus, density is not onlyphysical, but also sociological, economic, mathematical and geographical. Knowing the initial parameters of the substance, it is very simple to calculate the density indicator. This is done in just one action. Most often, the concept of density is found in the school curriculum.