Multiples and Prefixes

T SLE 6.2 Ttie List of Decimal Multiples and Prefixes Used with SI Base Units... 

SI is a decimal system. Fractions have been eliminated, and multiples and submultiples are formed by a system of prefixes ranging from yotta, for 10 , to yocto, for 10 . Calculations, therefore, are greatiy simplified. 

Prefixes. In SI, 20 prefixes are used and are direcdy attached to form decimal multiples and submultiples of the units (see the introduction to this volume, p. xvi). Prefixes indicate the order of magnitude, thus eliminating nonsignificant digits and providing an alternative to powers of 10 eg, 45 300 kPa becomes 45.3 MPa and 0.0043 m becomes 4.3 mm. 

The Systeme International d Unites (International System of Units) has the abbreviation SI. It includes base units, supplementary and derived units which together form a coherent system of units. Prefixes are used to form decimal multiples and sub-multiples of the SI units. 

The metric measurement system is extremely easy to use, because all the units and equivalents are powers of 10. A kilogram is 1,000 times as big as a gram, and a centimeter is 0.01 as big as a meter. The multiplication and division problems using metric measures are really a piece of cake. When you learn what the different prefixes stand for, you can navigate your way through the metric measurement system. 

TABLE 11.3 Prefixes for Naming Multiples and Submultiples of Units... 

Appendix 5. Units of Radioactivity and Prefixes for Multiple Units in the International System... 

The International System (SI) of the Units rests upon seven base units and two supplementary units as shown in Table A-l. From the base units, derived units can be obtained to express various quantities such as area, power, force, etc. Some of these have special names as listed in Table A-2. Multiples and submultiples are obtained by using prefixes as shown in Table A-3. 

Table A-3 Multiples and Submultiples Multiplier Exponent Form Prefix SI Symbol...

Decimal multiples and submultiples of units may be indicated by the use of prefixes as defined in section 3.6 below. 

To signify decimal multiples and submultiples of SI units the following prefixes may be used [3]. 

The names and symbols of decimal multiples and submultiples of the SI base unit of mass, the kg, which already contains a prefix, are constructed by adding the appropriate prefix to the word gram and symbol g. 

The metric system and its more modem counterpart SI (for Systeme International d Unites) are systems of units designed to make calculations as easy as possible. It was designed to make every word mean one and only one thing. Its subdivisions and multiples of units are powers of 10 times a primary unit. Each of its prefixes means the same thing, no matter what unit it is attached to. The abbreviations for the quantities and prefixes are easy to remember. All these features have been built into the metric system to make it easy. Contrast this lack of ambiguity with the ambiguity in the English system, as illustrated in Example 2.4. 

Among the base units of the SI system, the kilogram unit of mass is the only one whose name, for historical reasons, contains a prefix Qdlo-). Names and symbols for multiples of the unit of mass are formed by attaching prefix names to the unit gram and prefix symbols to the unit symbol g. For example, 1(T kg = 1 mg (1 milligram) but not Ipkg (1 microkilogram). 

Decimal multiples and fractions of SI units are designated by prefixes. Those in common use are listed in Table 1.1. Thus we have, for example, that 1 cm = 10" m and 1 kg = 10 g. 

The trivial names of the aldoses can be used as prefixes to determine the stereochemistry for other chiral compounds. However, in this case, the -ose suffix is omitted and the prefix is written in italics (Figure 2.8). In this respect, it should be mentioned that the chiral centers can be separated by one or more nonchiral centers. If the number of chiral centers exceeds four (e.g., in heptose, octose, nonose, etc. derivatives), a multiple configurational prefix is added to the stem name (Figure 2.9). In this case, the first four chiral centers are selected, followed by the remaining ones. However, the name of the compound starts with the prefix of the chiral center with the highest location. In the case of ketoses, if the carbonyl group is not at C-2, then its location should also be given in the name. 

One of the best features of the SI system is that (except for time) units and their multiples and submultiples are related by standard factors designated by the prefixes indicated in Table 1.4. Prefixes are not preferred for use in denominators (except for... 

Decimal Multiples and Submultiples of SI Units In practical application of SI units, certain values are too large or too small to be expressed conveniently in the base or derived units. Numerical values can be brought to convenient size when the unit is appropriately modified by official SI prefixes. In general the prefixes are such that the value of the unit changes 1000-fold. However, certain common previously accepted multiples or sub multiples, such as deci- and hecto-, are still accepted in the SI framework. The SI prefixes are listed in Table 1-5 together with their symbols. 

The same prefixes are used with mass as with distance, and they have the same meanings. That is one facet that makes the metric system so easy. In the English system, the subdivisions of a yard are a foot—one-third of a yard—and an inch—one-thirty-sixth of a yard. The subdivision of an Avoirdupois pound is an ounce, one-sixteenth of a pound. The subdivision of a Troy pound is an ounce, one-twelfth of that pound. (Gold and silver are measured in Troy ounces.) Each type of measurement has a different subdivision, and none is a multiple of 10. The metric system uses the same prefixes for all types of measurements, they are all multiples of 10, and they always mean the same thing. The symbols for the units and prefixes are easier to learn than those for the English system units. For example, pound is abbreviated lb and ounce is oz, whereas the metric prefixes are almost always closely related to their names. It is easier to convert metric measurements because the prefixes mean some multiple of 10 times the fundamental unit. 

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