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Unit 1 Scientific Measurement Homework Read pages 11-13 HW: Unit 1 Significant Figures Quiz: October 1st or 2nd Qualitative Measurements Give results in a descriptive, nonnumeric form: hot cold big little heavy light short tall Qualitative measurements are often influenced by the measurer’s perception. Quantitative Measurements Give results in a definite form, typically a number with units: 100 °C 32 °F 10 gal. 30 ml 11.4 g/cm3 0.5 g/cm3 10 ft. 3 ft. A quantitative measurement is only as accurate as the instrument and method used to take the measurement. Accuracy and Precision Accuracy - a measure of how close a measurement is to the true value of whatever is being measured Precision – a measure of how close a series of measurements are to one another Significant Figures In Mathematics all numbers are exact; for example: 1 = 1.00 = 1.000000 In Science, numbers that are from data that is measured or calculated from measurements, are limited in the number of significant figures they can use. 1 ≠ 1.00 ???? Significant figures The significant figures in a measurement include all of the digits that are known. Calculated values depend on the number of significant figures in the values used in the calculations. Significant Figures For Example: Using a meter stick, that has markings 1mm apart, to measure the diameter of a can you might get 38 mm. Using calipers, that read to .01 mm, to measure the same can, you might get 37.79 mm. The caliper measurement has more significant figures than the meter stick measurement. Significant figures Rules of significant figures: Any nonzero digit (1,2,3,4,5,6,7,8,9) is significant. Example: 23.5 has 3 significant figures Any zero that is sandwiched in between two nonzero digits is significant. Examples: 3200.04 has 6 significant figures 403.2 has 4 significant figures Significant figures Zeros in front of non-zero numbers are not significant. Zeros at the end of a number without a decimal point are not significant Examples: 0.00079 and 650,000 each have 2 significant figures. Significant figures A zero to the right of the rightmost nonzero digit : a) Is significant if there is a decimal anywhere in the number. Examples: 0.0000000040 has 2 significant figures 973.4000 has 7 significant figures b) Is not significant if there is no decimal in the number. Examples: 10,000 has 1 significant figure 5960 has 3 significant figures Significant figures Some numbers are exact numbers, and have an infinite amount of significant figures. Example: Integers, the results of counting, are exact. 2 whole apples, means exactly 2, or 2.0000000000... to infinity. Significant Figures Some numbers can only be expressed with scientific notation!!! Example: Express 1000 with 2 significant figures. 1000 – has only 1 sig. fig. 1000.- has 4 sig. figs. 1.0 x 10³ has 2 sig. figs. Unit 1 – Sig Figs 2a. qual b. qual c. quant d. both 3. Lisa – not accurate or precise Lamont – accurate and precise Leigh Ann – precise, not accurate 4a. 3 b. 2 c. 4 d. 4 e. 3 f. 3 5a. 98.5 L b. 0.000763 cg c. 57.0 m d. 0.00750 mm