Seven basic SI units

The statutory units for measurements are based on the seven basic SI units of the Systeme International (SI). 

Except for temperature and time, nearly all scientific measurements are based on the metric system. In recent years, there has been a concerted international effort to persuade scientists to express all metric measurements in terms ofjust seven basic units, called SI units (for Systeme International). In addition to the seven basic SI units, there are seventeen other common units derived from them that have special names. However, despite the logical arguments that have been put forth for undeviating adherence to SI units, there has not been a strong popular move in this direction. For one thing, each scientist must cope... 

Many quantities you can measure need units other than the seven basic SI units. These units are derived by multiplying or dividing the base units. For example, speed is distance divided by time. The derived unit of speed is meters per second (m/s). A rectangle s area is found by multiplying its length (in meters) by its width (also in meters), so its unit is square meters (m ). 

There are seven basic SI (Systeme International) emits from which all other units can be derived. These seven are assumed to be independent of each other and have various specific definitions that you should know for the examination. The acronym is SMMACKK. The base SI units ... 

A dimensional system consists of all the primary and secondary dimensions and corresponding measuring units. The currently used International System of Dimensions (Systeme International d unites, SI) is based on seven basic dimensions. They are presented in Table 1 together with their corresponding basic units. For some of them a few explanatory remarks may be necessary. 

SI (Systeme International, International System of Units)—metric-based system of weights and measures adopted in 1960 by the 11th General Conference on Weights and Measures, in which 36 countries, including the U.S., participated. SI consists of seven basic units ... 

SI units fall into two groups basic units and derived units. The basic units are the seven mutually independent units (see Table 1) and include the meter, kilogram, second, ampere, kelvin, mole, and candela. They represent,... 

Temperature, one of the seven basic physical quantities of the International System (SI) of units, is that property which describes the thermodynamic states of a system and is a measure of that system s hotness, as expressed in terms of any of several arbitrary scales. It is an indicator of the direction in which energy will flow spontaneously when two bodies are brought into contact, that is, from the hotter body to the colder one. Temperature, unlike mass and volume, is an intensive property, that is, it is independent of the quantity of matter. 

In the SI system the seven basic units fisted in Table 1.2-1 are identified and their values are assigned. From these seven basic well-defined units, the units of other quan-dties can be derived. Also, certain quantities appear so frequently that they have been given special names and symbols in the SI system. Those of interest here are listed in Table 1.2-2. Some other derived units acceptable in the SI system are given in Table 1.2-3, and Table 1.2-4 lists the acceptable scaling prefi.xes. [It should be pointed out... 

The International System of Units (Systeme International SI) was adopted in 1960 by the General Conference of Weights and Measures as a coherent system based on seven basic units the meter, kilogram, second, ampere, kelvin, candela, and mole. In human medicine, the system has not been adopted universally. 

For historical reasons a number of different units of measurement have evolved to express a quantity of the same thing. In the 1960s, many international scientific bodies recommended the standardisation of names and symbols and the adoption universally of a coherent set of units — the SI units (Syst me Internationale d Unitds) — based on the definition of seven basic units, namely metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). 

The SI might be useful from the point of view of technology and metrology, but from the point of view of pure physics four out of its seven basic units are evidently derivative ones. 

The International System of Units (SI nnits) was established in 1960 by the International Bnrean of Weights and Measures. The system was established in an attempt to streamline the metric system, which included certain traditional units that had historical origins bnt that were not logically related to other metric units. The International System estabhshed fundamental units to represent seven basic physical quantities. These quantities and the fundamental units used to express them are given in Table A.I. 

The International System of Units (SI) is the modem metric system of measurement. The abbreviation SI is derived from the French Le Systeme International d UniUs. The ll" General Conference on Weights and Measures (CGPM, Confirmee Ginirale des Poids et Mesures) estabhshed the system in 1960. The seven basic units in the SI system are shown in Table 1.2, the recommended prefixes in Table 1.3 and derived units of general character are shown in Table 1.4. Some constants of importance for this book are collected in Table 1.5. These tables are collected at the end of this chapter (see pp. 14ff.). 

Table 1-4 gives the seven basic quantities assumed to be mutually independent, on which the SI is founded and the names of the respective units, called SI base units. 

The development of the metric system, which served as the basis of the International System of Units (Le Systeme International d Unites known as SI), occurred during the French Revolution in the mid-eighteenth century. This coincided with the beginning of the age of modern science, especially chemistry and physics, as the value of physical measurements in the conduct of those pursuits became apparent. As scientific activities became more precise and founded on sound theory, the common nature of science demanded an equally consistent system of units and measurements. The units in the SI have been defined by international accord to provide consistency in all fields of endeavor. The basic units are defined for only seven fundamental properties of matter. All other consistent units are derived as functions of these seven fundamental units. 

In the next section, we will introduce the standards for basic units of measurement. These standards were selected because they are reproducible and unchanging and because they allow us to make precise measurements. The values of fundamental units are arbitrary. In the United States, all units of measure are set by the National Institute of Standards and Technology, NIST (formerly the National Bureau of Standards, NBS). Measurements in the scientific world are usually expressed in the units of the metric system or its modernized successor, the International System of Units (SI). The SI, adopted by the National Bureau of Standards in 1964, is based on the seven fundamental units listed in Table 1-5. All other units of measurement are derived from them. 

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