Specific gravity

Probably, there is no schoolboy who did not hear the following task: "What is easier - a kilogram of down or a kilogram of bricks?". The most interesting thing is that, despite the verbal absurdity, very many get involved in a useless argument. When the specific weight appeared in public practice, it is not known, but it can be assumed that the evaluation of the weight data of surrounding objects on the basis of a comparison of their volumetric characteristics has been known since the time of Archimedes. Specific characteristics are understood as the ratio of some measured quantities, say, weight and volume. The specific weight G is calculated through the relation:

G = P / V, and the unit of measurement in SI - n / m cu.

Weight is a measure of Earth gravitation, and the specific gravity for this reason is not a physical characteristic of substances, as it depends on the place of measurement. From what does it follow? Recall that the weight P is the force characteristic of the gravitational field, which is related to the inertial characteristic of the substance, mass m, through the acceleration of gravity g. On the other hand, g is a non-constant value, and depends, in part, on geographic coordinates. Since Newton's first law P = m * g is always valid, we can conclude about the variability of weight simultaneously with the change in the acceleration of gravity.

The classical definition is: "The specific weight is the ratio of body weight to its volume." However, in this simplicity there is quite a significant complexity - an incorrect application of units of measurement led to a confusion of concepts related to the mass and weight of the body. As is known, the system unit of mass (SI) is 1 kg, and the force in this system, according to Newton's law, is measured in newtons, with IH = 0.102 kg * 9.8 m / sec. Sq. M.

For many technical applications, the Newton force unit is somewhat inconvenient, so even went for the creation of a new measurement system - ICGSS. It included mixed units of measure: meter - kg-force - second. What does this give? Simplifies the use of units of force in real life due to the same numerical expression of specific gravity and specific gravity, i.e. Density in different systems, provided that the acceleration g is constant, or negligible.

The need to use specific gravity is in demand in technologies for identifying materials, determining the impurities in them or the porosity of the structure.

Well-known method for determining the sample of gold, the density of the structure of precious stones, etc. The main way to carry out measurements of specific gravity is based on different displacement options: the body weight is measured and, by immersion in water, its volume, and the rest is said to be a matter of technology. The use of data obtained in this way is especially effective when studying metals and their alloys. Usually, a priori, the specific weight of metals with well-studied properties is known. Their identity with new samples is established by many indicators, but the study begins with a measurement of specific gravity.

As a liquid, water is usually used, and when measuring high accuracy, it is ensured by a high stability of external parameters - temperature and pressure. Sometimes, for example, when investigating amber for the purpose of forgery, special fluids with a specific gravity of more than 2 g / cm3 are used.

The specific weight became the main technological element in the introduction of magnetic liquids into industrial production . A finely dispersed kerosene suspension with a ferro-powder makes it possible to create a fluid with a variable controlled or predetermined specific gravity with the help of a magnetic field. For such a technological process, enrichment of polymetallic ores and many other materials with a large number of impurities, which are separated by layers of the flotation bath in accordance with their individual specific gravity, are on hand. It is possible that for such environmentally friendly technologies of ore dressing - a great future.