Chapter 16. Units

Chapter 16 Units 16.1 History of Units    A common denomination of units is essential for the development of trade and economics around the world National Bureau of Standards, established by Congress, adopted the English system of measurement (12 inches, etc) Majority of nations in the world today operate on the metric system because of its simplicity (multiples of 10) 16.1 History of Units - SI Units   Le Systeme International d’Unites, French for the International System of Units Improvements in the definitions of the base units continue to be made by the General Conference of Weights and Measures as science dictates 16.2 The SI System of Units    Modernized metric system adopted by the General Conference, a multinational organization which includes the United States Built on a foundation of seven base units, plus two supplementary ones All other SI units are derived from these nine units 16.2 The SI System of Units   Multiples and sub-multiples are expressed using a decimal system Generally, the first letter of a symbol is capitalized if the name of the symbol is derived from a person’s name, otherwise it is lowercase 16.2 The SI System of Units  Base Units in the SI system        Meter = m Kilogram = kg Seconds = s Ampere = A Kelvin = K Mole = mol Candela = cd 16.3 Derived Units   Expressed algebraically in terms of base and supplementary units Several derived units have been given special names and symbols, such as the newton (N). 16.3 Derived Units  Quantities whose units are expressed in terms of base and supplementary units Quantity Area SI Unit Square meter Speed, Meter per velocity second Density Kilogram per cubic meter SI Symbol m2 m/s Kg/m3 16.3 Derived Units  Quantities whose units have special names Quantity SI Name SI Symbol Frequency hertz Hz Other SI Units cycle/s Force newton N kg*m/s2 Electrical Resistance ohm Ω V/A 16.3 Derived Units  Units used with the SI System Name Symbol Value in SI Units Minute min 1 min = 60 s Hour h 1 h = 3600 s Degree ° 1° = π/180 rad 16.4 Prefixes     Defined for the SI system Used instead of writing extremely large or very small numbers All items in a given context should use the same prefix, for example in a table Notation in powers of 10 is often used in place of a prefix 16.4 Prefixes Multiplication Prefix Symbol Factor M 1000000 = 106 mega Term (USA) One million 1000 = 103 kilo k One thousand .001 = 10-3 milli m One thousandth µ One millionth .000001 = 10-6 micro 16.5 Numerals  A space is always left between the numeral and the unit name or symbol, except when we write a degree symbol   SI units a space is used to separate groups of three in a long number    3 m = 3 meters; 8 ms = 8 milliseconds 3,000,000 = 3 000 000 .000005 = .000 005 This is optional when there are four digits in a number (3456 = 3 456; .3867 = .386 7) 16.5 Numerals    A zero is used for numbers between -1 and 1 to prevent a faint decimal point from being missed Rounding Significant Digits 16.6 Conversions To convert from: To: Multiply by: Degrees Radians 0.017 453 Inches Centimeters 2.54 Newtons Pounds 0.224 81