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Appendix 1 - Units and Converstion Factors

  • Page ID
    52104
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    testing

     

    Wherever possible, this text uses metric units of measurement. The metric system of measurement is used by all major countries but the United States, and it is the universal system used by all scientists. At present, an additional process is under way directed toward using only those metric units that are standard units approved in the International System of units (SI units). However, some of these standard units are unfamiliar even to many scientists, so they are not yet universally used. SI units are used in this text if they are generally in wide usage. In some instances where nonstandard units are much more widely used in the United States, the nonstandard units are used in this text. Over time, there will likely be a migration to the universal and exclusive use of SI units. The SI unit system has only seven base units from which all other units are derived (derived units are combinations of the base units). Tables listing the base units of the SI system, some derived SI units, and all of the units used in this text are included in this appendix. Some conversion factors to relate the SI units and other metric units to other units commonly used in the United States are also included.
    The scientific community almost universally uses exponential notation for numbers. Exponential notation is explained in Chapter 1 and is used throughout this text. This appendix includes a table (“Exponential Notation and the Decimal System”) for converting exponential numbers to their nonexponential equivalents. To multiply numbers expressed exponentially, add the exponents (superscript numbers). For example, 10–1 × 103 = 102 (one-tenth of 1000 is equal to 100). To divide, subtract the exponents. The “SI Base Units” table also lists the common terms used to identify certain exponent values. For example, 1000 is equivalent to 103, or 1 × 103, and 1000 can be expressed as “one thousand,” while other units can be prefixed by “kilo-” to express one thousand of the units; for example, 1 kilogram is equal to 1000 grams.
    Note that the naming system for large and small numbers is different in different parts of the world. In many non-English-speaking countries (and formerly in England), the term billion does not mean 109. Instead, in this alternate system billion is 1012 and trillion is 1018. This is one reason why it is always better to use exponential notation for large or small numbers.

    SI UNITS table

     

    Examples of Derived SI Units

    Derived Quantity Name Symbol
    Area square meter m2
    Volume cubic meter m3
    Speed, velocity meter per second m·s–1
    Acceleration meter per second squared m·s–2
    Mass density kilogram per cubic meter kg·m–3
    Specific volume cubic meter per kilogram m3·kg–1
    Current density ampere per square meter A·m–2
    Magnetic field strength ampere per meter A·m–1
    Amount-of-substance concentration mole per cubic meter mol·m–3
    Luminance candela per square meter cd·m–2
    Mass fraction kilogram per kilogram,
    which may be represented by the number 1
    kg·kg–1 = 1

     

     SI Derived Units with Special Names and Symbols

    Derived Quantity Name Symbol Expression in Terms of Other SI Units Expression in Terms of SI Base Units
    Plane angle radian rad m · m–1 = 1
    Frequency hertz Hz s–1
    Force newton N m · kg · s–2
    Pressure, stress pascal Pa N · m–2 m–1 · kg · s–2
    Energy, work, quantity of heat joule J N · m m2 · kg · s–2
    Power, radiant flux watt W J · s m2 · kg · s–3
    Celsius temperature degree Celsius °C K
    Luminous flux lumen lm cd · sr m2 · m–2 · cd = cd
    Illuminance lux lx lm · m2 m2 · m–4 · cd = m–2 · cd
    Activity (of a radionuclide) becquerel Bq s–1
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