Standard SI Prefixes

The kilogram is the standard SI base unit for mass, even though it includes a multiplier prefix. However, for the application of other prefix multipliers the base word is the gram thus 1000 kilograms is 1 Mg, not 1 kkg. 

The use of the prefix symbol M is a cause of much confusion in the natural gas business. In standard SI Units, M means mega and... 

The International Organization for Standards (ISO) recommends that prefix symbols be printed in Roman (upright) type without spacing between the prefix symbol and the unit symbol, thus mL rather than m L. Furthermore, an exponent attached to a symbol containing a prefix indicates that the multiple or submultiple of the unit is raised to the power expressed by the exponent (e.g., cm is 10 m ). Compound prefixes formed by the juxtaposition of two or more SI prefixes are not to be used. Thus 1 nm is appropriate, whereas 1 m LLm is not. Likewise, the appropriate unit of mass is the megagram (Mg) rather than the kilokilogram (kkg). 

The metric system, or International System (SI, from Systlme International), is a decimal system of units for measurements of mass, length, time, and other physical quantities. Built around a set of standard units, the metric system uses factors of 10 to express larger or smaller numbers of these units. To express quantities that are larger or smaller than the standard units, prefixes are added to the names of the units. These prefixes represent multiples of 10, making the metric system a decimal system of measurements. Table 2.1 shows the names, symbols, and numerical values of the common prefixes. Some examples of the more commonly used prefixes are... 

It is often necessary to form decimal multiples and submultiples of the SI unit, in order to avoid very large or very small numbers, respectively. These multiples, called SI prefixes, are summarized in O Table 11.9, where the standard notations are also given. A prefix attaches directly to the name of the unit, and a prefix symbol attaches directly to the symbol for a unit. For example, one kilometer (symbol 1 km) is equal to one thousand meters, symbol 1,000 m or 10 m. 

Metric units in equations will follow SI metric practice. To avoid confusion, values in the text that are also used in equations will use standard SI units even if more reasonable numeric values are possible with prefixes. Units for variables in U.S. engineering units (U.S. Eng.) are shown in brackets []. Units for variables in metric units (Metric) will be shown in braces. The nomenclature list shows both U.S. engineering units and metric units used in the equations. Care must be taken to use the correct units, since several equations contain dimensional constants. Results can be incorrect if the wrong units are used. 

Standard meter bar an unchanging, reproducible quantity 1 meter is the distance traveled by light in a vacuum in 1/299,792,458 of a second. Length is one of the seven fundamental quantities in the SI system (see Table 1.1). All other physical quantities have units that can be derived from these seven. SI is a decimal system. Quantities differing from the base unit by powers of ten are noted by the use of prefixes. For example, the prefix kilo means "one thousand" (10 ) times the base unit it is abbreviated as k. Thus 1 kilometer = 1000 meters, or 1 km = 1000 m. The SI prefixes are listed in Table 1.2. 

For many purposes, the chosen unit in the SI system will be either too large or too small for practical purposes, and the following prefixes are adopted as standard. Multiples or sub-multiples in powers of 103 are preferred and thus, for example, millimetre should always be used in preference to centimetre. 

The metric system, or Systeme International d Unites (SI system as it is commonly known), is the predominant system of measurement in the world. In fact, the United States is one of only about three countries that do not commonly use the metric system. The metric system attempts to eliminate odd and often difircult-to-remember conversions for measurements (5,280 feet in a mile, for example). It is a decimal-based system with standard terminology for measurements of length, volume, and mass (weight). It also uses standard prefixes to measure multiples of the standard units. 

TABLE 2. STANDARD prefixes USED WITH SI units ... 

To express quantities much larger or smaller than the standard units, multiples or submultiples of these units are used, as shown in the Table 1-1. Thus, lO12 s is a picosecond (ps), and 103 m is a kilometer (km). Since for historical reasons the SI reference unit for mass, the kilogram, already has a prefix, multiples for mass should be derived by applying the multiplier to the unit gram rather than to the kilogram. Thus lO9 kg is a microgram (KT6 g), abbreviated pg. 

The metric system consists of a base unit and (sometimes) a prefix multiplier. Most scientists and healthcare providers use the metric system, and you are probably familiar with the common base units and prefix multipliers. The base units describe the type of quantity measured length, mass, or time. The SI system is sometimes called the MKS (meter, kilogram, second) system, because these are the standard units of length, mass, and time upon which derived quantities, such as energy, pressure, and force, are based. An older system is called the CGS (centimeter, gram, second) system. The derived CGS units are becoming extinct. Therefore, we will focus on the MKS units. 

Time The SI base unit for time is the second (s). The frequency of microwave radiation given off by a cesium-133 atom is the physical standard used to establish the length of a second. Cesium clocks are more reliable than the clocks and stopwatches that you use to measure time. For ordinary tasks, a second is a short amount of time. Many chemical reactions take place in less than a second. To better describe the range of possible measurements, scientists add prefixes to the base units. This task is made easier because the metric system is a decimal system. The prefixes in Table 2-2 are based on multiples, or factors, of ten. These prefixes can be used with all SI units. In Section 2.2, you will learn to express quantities such as 0.000 000 015 s in scientific notation, which also is based on multiples of ten. 

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... 

The defining event of a radioactive nuclide is the transformation of its nucleus into the nucleus of another species, that is, radioactive decay. The number of nuclear transformations occurring per unit of time is called activity . Sometimes radioactivity is used instead of activity . The traditional unit of activity has been the Curie (Ci), which is equal to 3.7 X 10 ° nuclear transformations per second. The conversion of radiation units to the international system (Sysfme International d Unit or SI) has now taken place in the United States. The more fundamental unit of activity, the Becquerel (Bq), equal to 1 nuclear transformation per second, has replaced the Curie. Both units of activity are modified by prefixes such as kilo-, milli-, and micro- to achieve standard multiples of the fundamental unit. A listing of the most commonly used prefixes is given in Table 1. 

The SI system also employs standard prefixes for each unit. These prefixes are commonly seen on the MCAT. The table below lists these standard prefixes ... 

The SI emit for measuring pressure is the pascal (Pa), named after the French physicist Blaise Pascal (1623-1662). Because the pascal is a small pressure emit, it is more convenient to use the Idlopascal. As you recall from Chapter 1, the prefix kilo- means 1000 so, 1 Idlopascal (kPa) is equivalent to 1000 pascals. One standard atmosphere is equivalent to 101.3 Idlopascals. 

Multiples and submultiples of SI units are commonly used. Examples are the millimeter and kilometer. These multiples and submultiples are denoted by standard prefixes attached to the name of the unit, as listed in Table 1.3. The abbreviation for a multiple or submultiple is obtained by attaching the prefix abbreviation... 

Mass The mass of an object refers to the quantity of matter it contains. The SI unit of mass is the kilogram (kg), the only base unit whose standard is a physical object—a platinum-iridium cylinder kept in France. It is also the only base unit whose name has a prefix. (In contrast to the practice with other base units, however, we attach prefixes to the word gram, as in microgram, rather than to the word kilogram thus, we never say microkilogram. )... 

Certain SI derived units have special names and symbols these are given in Table A.3. Table A.4 presents examples of SI derived units expressed with the aid of SI derived units having special names and symbols. Table A.5 presents standard prefixes. 

SI units (Systeme fntemational d Unites) The internationally adopted system of units used for scientific purposes. It has seven base units and two dimensionless units, formerly called supplementary units. Derived units are formed by multiplication and/or division of base units. Standard prefixes are used for multiples and submulti-... 

The following SI (International System of Units) and non-SI units are used in the transportation regulations. The SI system is based on fundamental standards, derived units, and prefixes. 

The text has employed, as far as possible, the internationally accepted units of the Systeme International d Unites (SI Units). Some of the source material, however, was expressed in other units and has been quoted as such. This appendix shows the connections and lists the standard prefixes of size. 

The internationalization of science and engineering led to the establishment of a standard system that provides the needed flexibility to handle a wide array of observations. In this International System of Units (Systhne International d Unites, or SI), carefully deflned units are combined with a set of prefixes that designate powers of ten. This allows us to report and understand quantities of any size, as illustrated in Figure 1.8. 

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