In the world there were and still are many different systems for measuring quantities. They serve to enable people to exchange various information, for example, when making transactions, prescribing drugs or developing guidelines for the use of technology. In order to avoid confusion, an international system for measuring physical quantities was developed.
What is a physical quantity measurement system?
Such a concept as a system of units of physical quantities, or simply a SI system, can often be found not only in school physics and chemistry lessons, but also in everyday life. In the modern world, people more than ever need certain information - for example, time, weight, volume - to be expressed most objectively and structured. It is for this that a unified system of measurements was created - a set of officially accepted units of measurement recommended for use in everyday life and science.
What measurement systems existed before the advent of the SI system
Of course, a person always had a need for measures, however, as a rule, these measures were not official, they were determined through improvised materials. So, they did not have a standard and could vary from case to case.
A striking example is the system of length measures adopted in Russia. Span, elbow, arshin, fathom - all these units were originally attached to parts of the body - palms, forearms, the distance between outstretched arms. Of course, as a result, the final measurements were inaccurate. Subsequently, the state made efforts to standardize this system of measurement of quantities, but it still remained imperfect.
Other countries had their own systems for measuring physical quantities. For example, in Europe, the English system of measures was widespread - feet, inches, miles, etc.
Why do we need a SI system?
In the XVIII-XIX centuries, the process of globalization became active. More and more countries began to establish international contacts. In addition, the scientific and technological revolution has reached its peak. Scientists around the world could not effectively share the results of their scientific research due to the fact that they used different systems for measuring physical quantities. Largely because of such disturbances in the bonds within the world scientific community, many physical and chemical laws were "discovered" several times by different scientists, which greatly impeded the development of science and technology.
Thus, the need arose for a unified system of measuring physical units, which would not only allow scientists around the world to compare the results of their work, but also optimize the process of world trade.
History of the International Measurement System
In order to structure physical quantities and the measurement of physical quantities, a system of units, common to the entire world community, has become necessary. However, creating such a system that would meet all the requirements and be the most objective is a really difficult task. The future SI system was based on the metric system, which became widespread in the 18th century after the French Revolution.
The starting point at which the development and improvement of the International System for Measuring Physical Quantities began and can be considered June 22, 1799. It was on this day that the first standards were approved - a meter and a kilogram. They were made of platinum.
Despite this, the International System of Units was officially adopted only in 1960 at the 1st General Conference on Weights and Measures. It included 6 basic units of measurement of physical quantities: second (time), meter (length), kilogram (mass), kelvin (thermodynamic temperature), ampere (amperage), candela (luminous intensity).
In 1964, the seventh value was added to them - the mole, which measures the amount of substance in chemistry.
In addition, there are also derived units that can be expressed through basic ones using simple algebraic actions.
Basic SI units
Since the basic units of the system of physical quantities should be as objective as possible and not depend on external conditions, such as pressure, temperature, distance from the equator, and others, the formulation of their definitions and standards should be taken fundamentally.
Consider each of the basic units of a system for measuring physical quantities in more detail.
- Second. The unit of time. This value is relatively easy to express, since it is directly related to the period of the Earth's revolution around the Sun. Second is 1/31536000 of the year. However, there are more sophisticated ways to measure the second standard associated with periods of emission of a cesium atom. This method minimizes the error, which requires a modern level of development of science and technology.
- Meter. Unit of length and distance. At different times, they tried to express the meter as part of the equator or using a mathematical pendulum, but all of these methods were not accurate enough, so the final value could vary within millimeters. Such an error is critical, therefore, for a long time, scientists have been looking for more accurate ways to determine the standard meter. At the moment, the length of the path traveled by light in (1/299 792 458) seconds is taken as one meter.
- Kilogram. Unit of mass. Today, a kilogram is the only value determined through the material standard, which is stored at the headquarters of the International Bureau of Weights and Measures. Over time, the standard slightly changes its mass due to corrosion processes, as well as the accumulation of dust and other small particles on its surface. That is why it is planned to express its value in the near future through fundamental physical properties.
- Kelvin. Unit of measurement of thermodynamic temperature. Kelvin is equal to 1 / 273.16 of the thermodynamic temperature of the triple point of water. This is such a temperature at which water is immediately in three states - liquid, solid and gaseous. Celsius degrees are converted to Kelvin by the formula: t K = t C ° + 273
- Ampere. The unit of current. An unchanging current passing through two parallel straight conductors with a minimum cross-sectional area and an infinite length located 1 meter apart from each other (a force of 2 × 10 -7 N arises in each section of these conductors) is 1 ampere.
- Candela. A unit of measurement of light intensity is the luminosity of a source in a certain direction. A specific quantity that is rarely used in practice. The value of unity is derived through the frequency of radiation and the energy intensity of light.
- Moth. Unit of amount of substance. At the moment, a mole is a unit that is different for different chemical elements. It is numerically equal to the mass of the smallest particle of this substance. In the future, it is planned to accurately express one mole using the Avogadro number. For this, however, it is required to clarify the meaning of the Avogadro number itself.
SI prefixes and what they mean
For the convenience of using the basic units of physical quantities in the SI system, in practice, a list of universal prefixes has been adopted, with the help of which fractional and multiple units are formed.
Derivative Units
Obviously, there are much more than seven physical quantities, which means that units are needed in which these quantities should be measured. For each new quantity a new unit is derived, which can be expressed in terms of basic ones using simple algebraic actions, for example division or multiplication.
Interestingly, as a rule, derivative units are named after great scientists or historical persons. For example, the unit of work is Joule or the unit of inductance is Henry. There are many derivative units — more than twenty in all.
Extra system units
Despite the widespread and widespread use of units of the system of physical quantities of SI, in many industries off-system units are still used in practice. For example, in shipping - a nautical mile, in jewelry - a carat. In everyday life, we know such non-systemic units as day, percent, diopter, liter and many others.
It must be remembered that, despite their familiarity, in solving physical or chemical problems, non-systemic units must be converted into units of measurement of physical quantities in the SI system.