Using Scientific Measurements 2.3

Accuracy vs. Precision Accuracy – the closeness of a measurement to the correct or accepted value of quantity measured. Precision – the closeness of a set of measurements of the same quantity made in the same way 4 darts clustered together = acc or pre?

Percent Error Always some error in a measurement Instrument, limits of measurer, calibrations % error – calculated by the following formula… % error = Valueexp – Valueacc x 100 Valueacc

Significant Figures Sig figs – all the digits known with certainty plus one final digit, which is somewhat estimated or uncertain Graduated cylinder example 42.5 mL - the 5 is the estimated number

Rules for Determining Sig. Figs. All non zero digits are significant No decimal = book end Decimal = go to 1st non zero and count everything to the right Exact numbers have infinite significant figures (1m = 1000mm) Calculators exaggerate precision

Sig. Fig Examples How many sig figs are in… 203000 1000.00 0.00052 0.06400 79.810

Significant Figures Multiplication and division sig. digs = answer has no more figs. than the msmt. with the least # of sig. figs. 12.257 5 #’s x 1.162 4 #’s 14.2426340 4 #’s = 14.24

Significant Figures Addition and subtraction = answer has no more numbers to the right of the decimal pt. than the number with the least numbers to the right of the decimal. 3.9 5 2.8 79 + 213.6 220.4 29 = 220.4

Scientific Notation 29640000000000000000000 copper atoms in 1 penny 2.964 x 1022 atoms 2 Parts to scientific notation # between 1 and 10 Power of 10

Scientific Notation 0.000000000000003332 kg 3.322 x 10-15 kg 1970000000 L 1.97 x 109 What is ….. In scientific notation? 4.58 x 105 9.05 x 10-3