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Significant digits, base, and derived units CMA High school Base units of the metric system Base quantity Length mass Time Temperature Amount of a substance Electric current Luminous intensity Base unit meter kilogram second kelvin mole symbol m kg s K mol ampere candela A cd Derived units • Derived units are combinations of base units. • Examples: speed= m/s • Density = kg/m3 • Momentum = kg m/s • Force = kg m/s2= Newton Significant digit rules • Nonzero digits are always significant • All final zeros after the decimal point are significant • Zeros between two significant digits are significant • Zeros used solely as placeholders are not significant Examples: • • • • • • 305940 = 5 sig digs 3.5000 = 5 sig digs 0.0000000000500 = 3 sig digs 4.002 = 4 sig digs 0.000000002 = 1 sig dig 120000000000 = 2 sig digs Adding and subtracting sig digs • Line up numbers with the decimal to add or subtract, then round the answer to the smallest number of significant digits after the decimal that you started with. • 24.686m + 2.343m + 3.21 m = 30.239 m • Round the answer to 30.24 m Multiplying and dividing sig digs • After multiplying or dividing, round your answer up to the smallest total number of significant digits that you started with. ( Don’t pay attention to the decimal) • 3.22 cm x 2.1 cm = 6.762 cm2, round up to 6.8 cm • 4596/ 1 = 4596, round your answer to 5000 Homework/ classwork • http://lectureonline.cl.msu.edu/~mmp/appli st/sigfig/sig.htm
