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Systems of Measurement • Why do we need a standardized system of measurement? –Scientific community is global –An international “language” of measurement allows ALL scientists to communicate Metric System & SI • The first standardized system of measurement: the “Metric” system – Developed in France in 1791 – Named based on French word for “measure” – based on the decimal (powers of 10) • Systeme International d'Unites (International System of Units) – Modernized version of the Metric System – Abbreviated by the letters SI. – Established in 1960, at the 11th General Conference on Weights and Measures. – Units, definitions, and symbols were revised and simplified. Components of the SI System • The SI system of measurement has 3 parts: –base units –derived units –prefixes SI: Base Units Physical Quantity Unit Name Symbol length meter m mass kilogram kg time second s electric current ampere A temperature Kelvin K amount of substance mole mol luminous intensity candela cd SI: Derived Units Physical Quantity Unit Name Symbol area square meter m2 volume cubic meter m3 speed meter per second m/s acceleration meter per second squared m/s2 weight, force newton N pressure pascal Pa energy, work joule J Prefixes Prefix Symbol Numerical Multiplier Exponential Multiplier yotta Y 1,000,000,000,000,000,000,000,000 1024 zetta Z 1,000,000,000,000,000,000,000 1021 exa E 1,000,000,000,000,000,000 1018 peta P 1,000,000,000,000,000 1015 tera T 1,000,000,000,000 1012 giga G 1,000,000,000 109 mega M 1,000,000 106 kilo k 1,000 103 hecto h 100 102 deca da 10 101 1 100 no prefix means: Prefixes Prefix Symbol no prefix means: Numerical Multiplier Exponential Multiplier 1 100 deci d 0.1 10¯1 centi c 0.01 10¯2 milli m 0.001 10¯3 micro m 0.000001 10¯6 nano n 0.000000001 10¯9 pico p 0.000000000001 10¯12 femto f 0.000000000000001 10¯15 atto a 0.000000000000000001 10¯18 zepto z 0.000000000000000000001 10¯21 yocto y 0.000000000000000000000001 10¯24 “Staircase” Method Problem: convert 114.55 cm to km Dimensional Analysis Factor-Label Method • Multiply by conversion factor (a fraction that relates the original unit and the desired unit) – Conversion factor is always equal to 1. – Numerator and denominator should be equivalent measurements. • When measurement is multiplied by conversion factor, original units should cancel Dimensional Analysis Factor-Label Method • Convert 6.5 km to m Convert 3.5 hours to seconds Units of Volume • • • • The space occupied by matter Derived from length (m3) Non-SI = Liter 1000 cm3 = 1 L 1 mL = 1 cm3 • Instruments: graduated cylinder, pipet, buret, volumetric flask Units of Temperature • Temperature – a measure of how hot or cold an object is (the avg. kinetic energy of particles in matter) • Heat flows from higher temp. to lower temp. • Substances expand as temp. increases (exception??) Celsius scale -freezing point of water = -boiling point of water = Kelvin scale -freezing point of water = -boiling point of water = 0 K (absolute zero) = -273.15°C K = °C + 273 °C = K - 273 Units of Energy • Joule (J) = SI unit of energy • Calorie (cal) 1 J = 0.2390 cal 1 cal = 4.184 J