There have been and still are many different measurement systems in the world. 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, the International System for the Measurement of Physical Quantities was developed.
What is a system for measuring physical quantities?
Such a concept as a system of units of physical quantities, or simply the SI system, can often be found not only in school lessons in physics and chemistry, but also in everyday life. In the modern world, people more than ever need certain information - for example, time, weight, volume - to be expressed in the most objective and structured way. It was for this that a unified measurement system was created - a set of officially accepted units of measurement recommended for use in everyday life andscience.
What measurement systems existed before the advent of the SI system
Of course, the need for measures has always existed in a person, however, as a rule, these measures were not official, they were determined through improvised materials. This means that they did not have a standard and could differ from case to case.
A vivid example is the system of measures of length adopted in Russia. A span, an elbow, an arshin, a sazhen - all these units were originally tied to parts of the body - the palm, forearm, the distance between outstretched arms. Of course, the final measurements were inaccurate as a result. Subsequently, the state made efforts to standardize this system of measurement, 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 common - feet, inches, miles, etc.
Why do we need the 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 apogee. 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 due to such violations of ties within the world scientific community, many physical and chemical laws were “discovered” several times by different scientists, which greatly hampered the development of science and technology.
Thus, there was a need for a unified system for 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 System of Measurement
In order to structure physical quantities and measure physical quantities, a system of units, the same for the entire world community, has become necessary. However, to create such a system that would meet all the requirements and be the most objective is a really difficult task. The basis of the future SI system was the metric system, which became widespread in the 18th century after the French Revolution.
The starting point from which the development and improvement of the International System for measuring physical quantities began can be considered June 22, 1799. It was on this day that the first standards were approved - the meter and the 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 (current), candela (light intensity).
In 1964, a seventh value was added to them - the mole, which measures the amount of a substance in chemistry.
In addition, there are alsoderived units that can be expressed in terms of basic ones using simple algebraic operations.
Basic SI units
Since the basic units of the system of physical quantities had to 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 had to be treated fundamentally.
Let's consider each of the basic units of the system of measurement of physical quantities in more detail.
Second. The unit of time. This is a relatively easy quantity to express, since it is directly related to the period of the Earth's revolution around the Sun. A second is 1/31536000 of a year. There are, however, more complex ways to measure the standard second, associated with the periods of radiation of the cesium atom. This method minimizes the error, which is required by the current level of development of science and technology
Meter. A unit of measure for length and distance. At various times, attempts were made to express the meter as part of the equator or with the help of a mathematical pendulum, but all these methods were not accurate enough, so that the final value could vary within millimeters. Such an error is critical, so for a long time scientists have been looking for more accurate ways to determine the meter standard. At the moment, one meter is the length of the path traveled by light in (1/299,792,458) seconds
Kilogram. Mass unit. To date, the kilogram is the only quantity defined through a real standard, whichkept 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 measure for thermodynamic temperature. Kelvin is equal to 1/273, 16 of the thermodynamic temperature of the triple point of water. This is the temperature at which water is in three states at once - liquid, solid and gaseous. Celsius degrees are converted to Kelvin by the formula: t K \u003d t C ° + 273
- Amp. A unit of current strength. An unchanging current, during the passage of which through two parallel straight conductors with a minimum cross-sectional area and infinite length, located at a distance of 1 meter from each other (a force equal to 2 10-7 arises on each section of these conductors H), is equal to 1 ampere.
- Candela. A unit of measurement for luminous intensity is the luminosity of a source in a particular direction. A specific value that is rarely used in practice. The value of the unit is derived through the frequency of radiation and the energy intensity of light.
- Moth. A unit of quantity of a substance. At the moment, the 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 express exactly one mole using Avogadro's number. To do this, however, it is necessary to clarify the meaning of the number itself. Avogadro.
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 was adopted, with the help of which fractional and multiple units are formed.
Derived units
Obviously, there are much more than seven physical quantities, which means that units are also needed in which these quantities should be measured. For each new value, a new unit is derived, which can be expressed in terms of the basic ones using the simplest algebraic operations, such as division or multiplication.
It is interesting that, as a rule, derived units are named after great scientists or historical figures. For example, the unit for work is Joule or the unit for inductance is Henry. There are many derived units - more than twenty in total.
Off-system units
Despite the widespread and widespread use of units of the SI system of physical quantities, non-system units of measurement are still used in practice in many industries. For example, in shipping - a nautical mile, in jewelry - a carat. In everyday life, we know such non-systemic units as days, percentages, diopters, liters and many others.
It must be remembered that, despite their familiarity, when solving physical or chemical problems, non-systemic units must be converted into units of measurementphysical quantities in the SI system.
