International System of Quantities

Table 1.1 lists not only the seven standard properties recognized by the International System of Quantities (SIQ) but also the symbols representing each property and its dimension as well as the base unit and its symbol. All other quantities may be derived from these base properties by multiplication and division (Bureau International des Poids et Mesures, 2006). For example, speed equals distance (or length) divided by time and is expressed as LjT. Several forms of energy have now been defined—Akinetic, potential, thermal, etc.—but energy was originally defined by Leibniz as the product of the mass of an object and its velocity squared. Thus, energy is expressed as MI /T ... 

The International System of Quantities is adopted in this section for the choice of units in our equations [66]. Also, so-called conventional units are introduced for those quantities for which other units are more frequently used (in place of the standard recommended) due to old habits and practice. 

The International System of Units (SI) provides a coherent system of measurement units, and all the physical quantities required for refrigeration and air-conditioning can he derived from the basic standards ... 

As you can see from this discussion, a wide number of different units can be used to express measured quantities in the metric system. Ibis proliferation of units has long been of concern to scientists. In 1960 a self-consistent set of metric units was proposed. This so-called International System of Units (SI) is discussed in Appendix 1. The SI units for the four quantities discussed are... 

All values of the IRMM Isotopic Reference Materials are traceable to the SI (the international system of base quantities and base units). Isotopic measurement results corrected by means of these Isotope Ratio Reference Materials have reduced (ISO/BIPM) uncertainties. Isotopic measruements carried out against these Spike Reference Materials are traceable to the SI, if carried out properly. Further details are available from IRMM website see Chapter 8. 

Becquerel (Bq)—International System of Units unit of activity and equals that quantity of radioactive material in which one transformation (disintegration) occurs per second (see Units). 

SI Units—The International System of Units as defined by the General Conference of Weights and Measures in 1960. These units are generally based on the meter/kilogram/second units, with special quantities for radiation including the becquerel, gray, and sievert. 

The ICRU (1980), ICRP (1984), and NCRP (1985) now recommend that the rad, roentgen, curie, and rem be replaced by the SI units gray (Gy), Coulomb per kilogram (C/kg), Becquerel (Bq), and sievert (Sv), respectively. The relationship between the customary units and the international system of units (SI) for radiological quantities is shown in Table D-5. 

M. A. Paul, International union of pure and applied chemistry. Manual of Symbols and Terminology for Physicochemical Quantities and Units, Butterworth, London, 1975. B. N. Taylor, ed.. The International System of Units, 7th ed., NIST Special Publication 330 (2001), http //physlab.nist.gOv/Pubs/SPS330/sps330.html. 

The concept and quantity absorbed dose were introduced by the ICRU in 1951, with the special unit rad. A new special unit gray (Gy) was introduced in 1972 to be in correspondence with the SI system of quantities and units (Systeme International des Grandeurs et Unites) [11,12]. 

In the text the recommendations made from the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Pure and Applied Physics (IUPAP) in respect to definitions (terms), symbols, quantities together with the International System of Units (SI) in respect to symbols in physical chemistry are considered.1... 

In this book SI (International System of Units) units are used fairly consistently in keeping with current practice. Some quantities are traditionally expressed in hybrid units —for example, the specific area is usually measured in m2 g "1 — and we continue this practice. The older literature uses cgs (centimeter-gram-second) units almost exclusively, so the reader must be cautious in consulting other sources. Appendix B contains a list of conversion factors between SI and cgs units. 

International System of Units, called SI units. The base system and the corresponding units and symbols are quantities of this... 

Here we propose the additional concepts under which analysts can formally substantiate and record their traceability link. A chain of such links should lead from the value of a quantity in a sample or reference material (RM) up to the value of a relevant unit in the International System of Units (SI) [5] or - where this is not possible - up to internationally agreed measurement scales. A protocol records specific details of scientifically reliable measurement procedures for the benefit of equity in trade and commerce, as well as for legal interpretations of scientific realities. Some ideas in this article go beyond established international understandings these are presented for debate and possible refinement. 

The International System of Units (SI) and Conversion Tables Quantity Unit SI Symbol... 

Among the advantages of the International System of Units system is that there is one, and only one, unit for any given physical quantity. Power, for instance, will always have the same unit, whether it has electrical or mechanical origins. 

We have seen that in the international system of units force is defined through Newton s law. Convenience dictates the introduction of a number of other defined quantities. Some, like volume, are so common as to require almost no discussion. Others, requiring detailed explanation, are treated in the following sections. 

The International System of Units is founded on seven base quantities (Table 3.1) that cover the whole field of natural science. Again, the system of quantities and equations of mechanics rests on the three base quantities length, mass and time, for which the units meter, kilogram and second are now internationally accepted. The derived unit of force is the Newton (N), being the force that gives the unit mass (kg) a unit acceleration (1 m s-2). The derived unit of energy is the Newton meter (N m). 

The International System of Units (SI) is based on seven base units for seven quantities. (One of these quantities is the mole.) The quantities are assumed to be all independent of each other. To learn about the seven base quantities, go to the web site above. Go to Science Resources, then to Chemistry 11 to find out where to go next. All other SI units are derived from the seven base units. 

The International System of Units (SI, Systeme International d Unites) is the most recent effort to develop a coherent system of units. It is coherent because there is only one unit for each base physical quantity, and units for all other quantities are derived from these base units by simple equations. It has been adopted as a universal system to simplify communication of numerical data and to restrict proliferation of systems. SI units are used by the National Institute of Standards and Technology (NIST). More information on SI can be found at http //www.physics.nist.gov/cuu/index.html. 

National Institute of Standards (NIST) Special Publication 330,2001 Edition, Engl, version of The International System of Units (SI), 7th ed. Bureau International des Poids et Mesures Sevres, France, 1998. http //physics.nist.gov/Pubs/SP330/sp330.pdf. Quantities and Units International Organization for Standardization Geneva, Switzerland, 1993. http //www.iso.org/iso/en/prods-service/ISOstore/store.html. 

Natural radionuclides contaminate air, food, and water. The annual per capita intake of natural radionuclides has been estimated to range from 2 Becquerels (Bq) for 232Th to about 130 Bq for 4 K (Sinclair 1988). The Bq is the International System of Units (SI) unit of radioactivity 1 Bq = 1 radioactive disintegration per second. The previously used unit of radioactivity is the Curie (Ci) 1 Ci = 3.7 x 1010 disintegrations per second, and 1 Bq = 27 x 10-12 Ci. The quantity of radiation or energy absorbed is expressed in Sievert (Sv), which is the SI unit of dose equivalent. The absorbed dose (in Gy) is multiplied by a quality factor for the particular type of radiation. Rem is the previously used unit for dose equivalent 100 rem = 1 Sv. 

Numbers and quantities should be expressed in units appropriate to the region into which the product is being supplied. In general, the International System of Units (SI) should be used. 

Because scientists work on scales ranging from the microscopic to the astronomical, there is a tremendous range in the magnitudes of measured quantities. Consequently, a set of prefixes has been incorporated into the International System of Units to simplify the description of small and large quantities (Table B.3). The prefixes specify various powers of 10 times the base and derived units. Some of them are quite familiar in everyday use the kilometer, for example, is 10 m. Others may sound less familiar—for instance, the femtosecond (1 fs = 10 s) or the gigapascal (1 GPa = 10 Pa). 

Why was the liter eliminated from the International System of Measurements Well, one of the goals of the conference was to cut down on the number of existing units and start off with the fewest number of base units that were needed to measure essentially all of the known physical quantities. Because volume can be expressed in cubed units of length, there really is no reason to support special units of volume. Following are the seven SI base units. 

Because of the nonstandard units associated with the I.U. system for defining enzyme concentrations, an equivalent International system of units (Systeme International) (S.I.) unit has been defined, and is called the katal. One katal (kat) of enzyme activity is that quantity that will consume 1-mol substrate/s 1 pkat = 60 I.U. 

Tab. 1.6 Base quantities, their dimensions and corresponding base units according to the currently valid International System of Dimensions, SI...

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