Have constant value, easy to preserve and reproduce, practical in size
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SI Base Units Quantity Quantity Symbol Unit Name Unit Abbreviation Length l meter m Mass m kilogram kg Time t second s Temperature T kelvin K Amount of substance n mole mol Electric current I ampere A
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SI Prefixes Prefix Unit Abbreviation Meaning/Example mega M 1Mm = 1,000,000m kilo k 1km = 1,000m hecto h 1hm = 100m deka da 1dam = 10m deci d 1m = 10dm centi c 1m = 100cm milli m 1m = 1,000mm micro μ 1m = 1,000,000 μ m nano n 1m = 1,000,000,000nm pico p 1m = 1,000,000,000,000pm
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Derived SI Units Quantity Quantity Symbol Unit Unit Abbreviation Derivation Area A Square meter m 2 length x width Volume V Cubic meter m 3 length x width x height Density D Kilograms per cubic meter kg/m 3 mass / volume Molar Mass M Kilograms per mole kg/mol mass / amount of substance Concentration c Moles per liter M amount of substance / volume Molar Volume V m Cubic meters per mole m 3 /mol volume / amount of substance Energy E joule J force x length
When you add or subtract decimals, the answer must have the same number of digits to the right as there are in the measurement having the fewest digits to the right of the decimal.
For multiplication and division, the answer can have no more sig. figs. than are in the measurement with the fewest number of sig. figs.
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