Presentation on theme: "Measurements: Every measurement has UNITS."— Presentation transcript:
1 Measurements:Every measurement has UNITS.Every measurement has UNCERTAINTY.
2 Accuracy and Precision in Measurements Accuracy: how close a measurement is to the accepted value.Precision: how close a series of measurements are to one another or how far out a measurement is taken.A measurement can have high precision, but not be as accurate as a less precise one.
3 Precision can also mean The number of decimal places assigned to the measured number (The more decimal places, the more precise the measurement)Ex.2.1 cm2.10 cm2.100 cm
4 the digit farthest to the right is considered to be estimated. Significant Figures are used to indicate the precision of a measured number or to express the precision of a calculation with measured numbers.In any measurementthe digit farthest to the right is considered to be estimated.122.01.3
5 Sig. Fig. Rules (with measurements): 1. All non-zero digits are significant.3 sig figssig figssig figs2. Zeros at the beginning of a measurement are not significant.sig figsig figssig figs
6 3. Zeros in between two significant figures are significant sig figssig figs4. Final zeros after a decimal point are significantsig figssig figssig figssig figssig figssig figsCounted numbers and definitions (2.54 cm = 1 inch) are considered to be exact and have no effect on the number of sig. figs. reported in calculations with measurements.
7 significant to the 0.1 place Calculations with sig. Figs.Addition and subtraction:Look at decimal places! Answer should have the same amount of decimal places as the measurement with the least amountcmcmcmcm= cmsignificant to the 0.1 place
8 Measurement Calculations with scientific notation. Addition/subtraction: must be placed into the same notation.(2.3 x 103) + (3.2 x 104) =0.23 x 104x 1043.43 x 104= 3.4 x 104
9 Calculations with Sig. figs. Multiplication and division (measurements):Count sig figs!!Answer should have the same amount of sig figs as the measurement with the least amount.2.734 cm x 5.2 cm x cm =cm34 s.f.2 s.f.5 s.f.written as 120 cm32 s.f.’s
10 1. The term that is related to the reproducibility (repeatability) of a measurement is a. accuracy.b. precision.c. qualitative.d. quantitative.e. property.Let’s take a “Quiz”b. precision.2. The number of significant figures in the mass measured as g isa. 1.b. 2.c. 3.d. 4.e. 5.e. 5.
11 3. The number of significant figures in 6.0700 x 10-4… is d. 6.e. 7.c. 5.4. How many significant figures are there in the value ?a. 7b. 6c. 5d. 4e. 3d. 4
12 Percent Error your value accepted value Indicates accuracy of a measurementyour valueaccepted value
13 Percent Error % error = 2.9 % A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.% error = 2.9 %