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Matter, Measurement, and Problem Solving Reliability of Measurement
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Reliability of a Measurement Scientific measurement is reported so that every digit is certain except the last one, which is estimated
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Sources of Error All measurements contain error Determinant error ◦ Consistent error- i.e. issues with calibration Indeterminate error ◦ Cause measurements to fluctuate around true value ◦ Factors beyond control Air currents, static, etc. ◦ Cannot completely eliminate
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Significant Figures in Measurements
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Rules for Significant Figures Exact numbers and definitions have infinite significant figures
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Practice Identifying Significant Figures 102.400 meters 1,200,000 g 4.3020 x 10 -8 m 2.030 x 10 5 nm 25 students 0.00090 cm 19 cm 3 2.05 x 10 7 g 13 eggs 2.37 x 10 -2 m 300,000,000 m/s 100 cm = 1 m
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Significant Figures in Calculations Two rules- ◦ addition and subtraction Place value of significant figures ◦ Multiply and divide Quantity of significant figures
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Addition and Subtraction Rules Result carries same number of decimal places as the quantity with fewest decimal places
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Addition Subtraction Practice 2.5 cm + 0.50 cm + 0.055 cm =
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Addition Subtraction Practice 416 g - 210 g =
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Addition Subtraction Practice 160 + 88.50
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Multiplying and Dividing Rule Result contains same number of significant figures as factor with fewest significant figures
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Multiplying and Dividing Practice 0.020 cm x 50 cm x 11.1 cm =
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Multiplying and Dividing Practice 0.530 g / 0.1010 mL =
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Multiplying and Dividing Practice 2.31 cm x 1.5 cm=
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Multiplying and Dividing Practice 1300 x 5.9980 =
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Precision vs. Accuracy Accuracy- how close the measured value is to actual value- how exact it is Precision- how close results are to one another
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Accuracy vs. Precision
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Percent Error Can apply to single measurement Expresses how much measurement deviates from true or accepted value
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Percent Error Practice At a track meet, you time a friend running 100 m in 11.00 seconds. The officials time her at 10.67 seconds. What is your percentage error?
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Error of Multiple Measurements Precision or reproducibility- calculate average
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Standard Deviation How much are the measurements off by?
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Example of Standard Deviation
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