DIFFERENTIATE: ACCURACY AND PRECISION

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Kerry Augustine Cameron
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1 DIFFERENTIATE: ACCURACY AND PRECISION

2 Can you hit the bull's-eye? Three targets with three arrows each to shoot. How do they compare? Both accurate and precise Precise but not accurate Neither accurate nor precise Can you define accuracy and precision? What would a bullseye with accuracy and no precision look like?

3 Significant Figures

What is a significant figure? There are 2 kinds of numbers: APPROXIMATE (OR MEASURED): weight, height, mass, distance anything MEASURED needs significance attached.

4 What is a significant figure? There are 2 kinds of numbers: APPROXIMATE (OR MEASURED): weight, height, mass, distance anything MEASURED needs significance attached. No measurement is perfect. EXACT (counted items and conversion factors have unlimited significant digits): the amount of money in your account, jelly beans in a jar, etc. And #m in a km or in in a ft

5 Reading a Meterstick. l I.... I 3....I.... I 4.. cm First digit (known) = 2 2.?? cm Second digit (known) = ? cm Third digit (estimated) between Length reported = 2.75 cm or 2.74 cm or 2.76 cm

6 Known + Estimated Digits In 2.76 cm Known digits 2 and 7 are 100% certain The third digit 6 is estimated (uncertain) In the reported length, all three digits (2.76 cm) are significant including the estimated one

7 When to use Significant figures To a mathematician 21.70, or is the same. But, to a scientist 21.7cm and 21.70cm is NOT the same

8 When to use Significant figures When a measurement is recorded only those digits that are dependable are written down.

9 Always estimate ONE place past the smallest mark!

10 Zero as a Measured Number. l I.... I I.... I 5.. cm What is the length of the line? First digit Second digit Last (estimated) digit is 5.?? cm 5.0? cm 5.00 cm

11 . l I.... I 9....I.... I 10.. cm What is the length of the line? 1) 9.6 cm 2) 9.62 cm 3) 9.63 cm How does your answer compare with your neighbor s answer? Why or why not? 1 0% 0% 0% 2 3

12 Significant Figures The numbers reported in a measurement are limited by the measuring tool Significant figures in a measurement include the known digits plus one estimated digit

13 Counting Significant Figures RULE 1. All non-zero digits in a measured number are significant. Only a zero could indicate that rounding occurred. Number of Significant Figures cm m kg m

14 How many sig figs in 65.8 kg % 0% 0% 0% 0%

15 How many sig figs in m % 0% 0% 0% 0%

16 Leading Zeros RULE 2. Leading zeros in decimal numbers are NOT significant. Number of Significant Figures mm mg kg ml

17 How many sig figs in kg % 0% 0% 0% 0%

18 How many sig figs in ml % 0% 0% 0% 0%

19 Sandwiched Zeros RULE 3. Zeros between nonzero numbers are significant. (They can not be rounded unless they are on an end of a number.) Number of Significant Figures 50.8 mm min kg m

20 How many sig figs in kg % 0% 0% 0% 0%

21 How many sig figs in m % 0% 0% 0% 0%

22 Trailing Zeros RULE 4. Trailing zeros in numbers without decimals are NOT significant. They are only serving as place holders. Number of Significant Figures 25,000 cm yr 3 48,600 L 25,005,000 g

23 How many sig figs in 48,600 L % 0% 0% 0% 0%

24 How many sig figs in 48,600. L % 0% 0% 0% 0%

How many sig figs in 25,005,000 g 1. 1 2.

25 How many sig figs in 25,005,000 g % 0% 0% 0% 0%

26 Which answers contain 3 significant figures? 1. ) ) ) % 0% 0% ) ) ) 4760

27 All the zeros are significant in , x % 0% 0% x 10...

28 534,675 rounded to 3 significant figures is , x % 0% 0% x 105

29 In which set(s) do both numbers contain the same number of significant figures? and and and 150,000 0% 0% 0% 22.0 and and and 1...

30 Significant Numbers in Calculations A calculated answer cannot be more precise than the measuring tool. A calculated answer must match the least precise measurement. Significant figures are needed for final answers from 1) adding or subtracting 2) multiplying or dividing

31 Adding and Subtracting The answer has the same number of decimal places as the measurement with the fewest decimal places one decimal place two decimal places answer 26.5 one decimal place

32 Learning Check In each calculation, round the answer to the correct number of significant figures. A = 1) ) ) 257 B = 1) ) ) 40.7

33 Multiplying and Dividing Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures.

34 Learning Check A X 4.2 = 1) 9 2) 9.2 3) B = 1) ) 62 3) 60 C X = X ) ) 11 3) 0.041

35 Learning Check State the number of significant figures in each of the following: A m B L C g D m E. 2,080,000 bees 3 5 7

36 How many sig figs? x ,000,

37 How many sig figs here? ,083,000,000 4

38 How many sig figs here? ,000,050,

39 Sig Figs?? 640 a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 0% 0% 0% 0% 0% 0%

40 Sig Figs?? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 0% 0% 0% 0% 0% 0%

41 Sig Figs?? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 0% 0% 0% 0% 0% 0%

42 Sig Figs?? a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 0% 0% 0% 0% 0% 0%

43 Sig Figs?? 10,000 a) 1 b) 2 c) 3 d) 4 e) 5 f) 6 0% 0% 0% 0% 0% 0%

44 How many sig figs?

45 How many sig figs here? 1.02 x x x x x x10 5 x

46 How many sig figs here? 23 x 2 x x 21 x x x x

47 Metric Prefixes

The Scientific Method & Experimental Design

The Scientific Method & Experimental Design Hypothesis: The increase in mass of a plant is dependent on the amount of carbon dioxide (CO 2 ) in the atmosphere. What is your independent variable(s)? What