Today it seems obvious that a kilogram of sugar in Russia and in Africa will be a kilogram of sugar. You will be surprised to learn that only 200 years ago 1 pound weighed differently even in neighboring provinces. We are led to a common denominator by the international SI system, which today operates in most countries of the world. But it was not always so. About the history of the introduction of measurement standards and a single SI system - further in the article.
Why do we need standards?
The development of civilization knew many standards and standards of measures that have been replaced over the centuries. For example, a measure of weight in ancient Egypt is kikkar, in ancient Rome - talent, in Russia - pood. And all these measures, replacing each other, required mankind to agree on uniform units of physical parameters that would be comparable to a single contractual unit (standard) for all.
With the development of scientific and technological progress, the need for such a unified system of standards only increased. Starting from the trade and economic sphere of activity, this system of standards has become a necessity in all other areas - construction (drawings), industrial (for example, unity of alloys) and even cultural (time intervals).
How the meter was determined
Almost until the end of the 17th century, length measures were different in different countries. But now the time has come when the development of science required a single measure of length - the Catholic meter.
The first standard was proposed by the British scientist and philosopher John Wilkins - to take the length of the pendulum, the half period of which is one second, as a unit of length. But it quickly became clear that this value varies greatly depending on the place of measurement.
In 1790, the National Assembly in France, at the suggestion of the then Minister Talleyrand, adopted one meter standard, in 1791 the French Academy of Sciences already accepted one ten-millionth part of the distance between the equator and the North Pole, measured according to the Paris Meridian, as a standard. Agree, it’s quite difficult.
The timid attempts continued
The prototype of the modern SI system was the metric system in France, which was proposed by the National Convention in 1795 to be developed by leading scientists of that time. Worked on the development of standards of length and mass Sh. Coulon, J. Lagrange, P.-S. Laplace and others. There were several proposals, but the meridian was still measured. And the first meter standard was made of brass in 1975.
And yet, the birthday of the unified system of measures and the prototype of the modern SI system of units should be considered June 22, 1799. It was then in France that the first standards of meter and kilogram were made of platinum.
Years go by, an absolute system of Gauss units (1832) and prefixes for designating multiple units of Maxwell and Thomson appear.
And so in 1875, 17 states signed the Metric Convention. It approved the International Bureau of Measures and the International Committee of Measures, and also launched its General Conference on Weights and Measures. At its first conference in 1889, the first unified metric system was adopted, based on meter, kilogram, second.
The history of standards continues
The development of electricity and optics makes adjustments to the concept of standards. Science does not stand still and requires ever new units of measurement.
In 1954, at the Tenth General Conference on Weights and Measures, six units were adopted - meter, kilogram, second, ampere, candela, Kelvin degree. In 1960, this system was called Systeme International d'Unites, and in 1960 the standard of the International System of Units, abbreviated SI, was adopted. The Russian-language “SI” stands for international system. This is the SI measuring system that the whole world uses today. The exceptions are the United States, Nigeria, Myanmar.
SI system definition
It should be noted right away that this is not the only system of standards. In some branches of applied physics, other unit systems are used.
Today, the SI International System of Physical Quantities is the most used metric system in the world. Its official detailed description is set out in SI Brochure (1970). The official definition is “The SI International System of Units is a system of units based on the International System of Quantities, together with names and designations, as well as a set of prefixes ... with application rules ...”.
System basis
The principles of SI units are as follows:
- Seven basic units of physical quantities are identified. In the SI system, they cannot be obtained from other quantities. This is kilogram (weight), meter (length), second (time), ampere (current), kelvin (temperature), mole (amount of substance), candela (light intensity).
- Derivatives are determined from the values of the basic SI system, which are obtained by mathematical operations with the basic quantities.
- Prefixes to quantities and rules for their use are defined. Prefixes mean that the unit needs to be divided / multiplied by an integer, which is a power of 10.
Significance in life and science
As already mentioned, most countries use SI system units. Even if in ordinary life they use units that are traditional for the country, they are determined by transferring them to the SI system using fixed coefficients.
All the basic units of the SI system are determined by physical constants or phenomena that are unchanged and can be reproduced anywhere in the world with high accuracy. The exception is only a kilogram, the standard of which so far remains the only physical prototype.
The ISS system of units (meter, kilogram, second) allows you to solve the problems of mechanics, thermodynamics and other areas of theoretical physics and practical science.
But in some industries (for example, in electrodynamics), the SI system loses to other metric systems. That is why there are several metric systems in the world, the values of which are more or less tied to the main standards - kilogram, meter and second.
SI units
The basic units (we recall - there are seven of them) and their designations are presented in the table, but they are familiar to all of us. The names of units in this system are written with a lowercase letter, and after the designation of units, a dot is not set.
Derivative units (there are 22) are expressed through mathematical calculus and follow from physical laws. For example, speed is the distance that a body travels per unit of time - m / s. Some derived units have their own names (radian, hertz, newton, joule) and they can be written in different ways.
There are units that are not part of the SI system, but are allowed to be shared. They are approved by the General Convention on Weights and Measures. For example, minute, hour, day, liter, knot, hectare.
It is also allowed to use units of logarithmic quantities, as well as relative ones. For example, percentage, octave, decade.
Allowed the use of and quantities that are widespread. For example, week, year, century.
For conveying values from different systems, developed convectors exist. There are a great many of them, but they all rely on uniform metric values.
Advantages of the SI International System
The versatility of this system is obvious. All physical phenomena, all branches of business and technology are covered by a single system of quantities. Only the SI system gives units that are important and easy to use.
The system is characterized by flexibility that allows the use of off-system units, and the possibility of development - if necessary, the number of SI values can be increased. Units can be adjusted in accordance with international agreements and the level of development of measurement technologies.
The unification of units has made this system applicable everywhere (in more than 130 countries) and recognized by many influential international organizations (UN, UNESCO, the International Union of Pure and Applied Physics).
The SI system increases the productivity of designers and scientists, simplifies and facilitates the educational process and the practice of international contacts in all areas.
The latest physical prototype
All units in the SI system are defined by physical constants. The exception is a kilogram. Only this standard so far has its own physical prototype and this stands out in a well-balanced line of units of measurement.
The kilogram standard is an alloy cylinder of 9 parts of platinum and 1 part of iridium. Its mass corresponds to one liter of water at its highest density (4 degrees Celsius, standard pressure above sea level). In 1889, 80 of them were manufactured, 17 of which were transferred to the countries that signed the Metric Convention.
Today, the original of this standard under three sealed capsules is in the city of Sevres on the outskirts of Paris in the safe of the International Bureau of Weights and Measures. Every year it is solemnly removed and reconciled.
The Russian version of the kilogram standard is in the All-Russian Research Institute of Metrology named after Mendeleev (St. Petersburg). These are prototypes No. 12 and No. 26.
Your iPhone will break due to the loss of the mass standard in the SI system
The whole metric system of mankind today is at risk. And this happens because just the only physically existing standard is rapidly "losing weight".
It has been experimentally proven that every century the standard kilogram becomes lighter by 3 x 10 −8 kilograms. This occurs due to the detachment of atoms at annual surveys. Obviously, violation of a constant of a given quantity will necessarily pull along with a change in all other quantities.
The project “Electronic kilogram” (National Institute of Standards and Technology, USA) is called to save the situation, which provides for the creation of a device of such power that can lift 1 kilogram of mass in an electromagnetic field. Work on the creation is underway.
Another direction is a cube of 2250 x 281489633 carbon-12 atoms. Its height will be 8.11 centimeters and it will not decrease over time. This project is also under development.
Interesting facts about the standards and not only
Time is a constant value. In all time zones of our planet, time is determined relative to UTC. It is interesting that this abbreviation has no decoding.
Sailors continue to use the unit "knot." Few people know, but this unit has a long history. To measure the speed of ships, a lag with knots tied at the same distance was previously used. Modern speedometers have become much more perfect, but the name remains.
And horsepower measurement of road transport is also based on real fact. The inventor of the steam engine, James White , demonstrated the advantages of his discovery. Under 1 horsepower, he counted the mass of load that the horse would lift per minute.