Monday’s Meanderings…

1. Monday’s Meanderings… • Open House tonight – bring a parent & your Buff Binder… drop your lowest grade!!! • Calculators - $10 see me quick! • Check your grade on the back wall – see me if you were absent for test and binder check Friday. Zeros highlighted can still be fixed. Tutorials: Tu, Th, Fr this week • Put page 18 on your handout for today. • Get out page 9 to TURN IN!!!

2. Significant Figures

3. Nature of Measurement Measurement - quantitative observation consisting of 2 parts • Part 1 – number • Part 2 - scale (unit) – NO NAKED NUMBERS! • Examples: • 20grams • 6.63 x 10-34Joule seconds

4. Significant Figures • All of the known digits + 1 estimated digit 7.21 cm

5. Uncertainty of Measurement • The last digit on any physical measurement is always an approximation. • Significant figures are the number of digits that can be accurately measured and the first uncertain digit.

6. Rule #1 • All non-zero numbers are significant (numbers 1-9) • 3.89 = __significant figures • 938.3 = ___ significant figures 3 4

7. Rule #2 • Sandwich rule: all zero’s between non-zero or significant numbers are significant • 202 = __ significant figures 3

8. Rule #2 8 • 67000045 = __ significant figures • 1.50098 = __ significant figures 6

9. Rule #3 • Leading zeros are NOT significant (zeros at the front of a 1-9 number)

10. Rule #3 Leading zeros are NEVER significant • 0.91 = ___significant figures • 0.0089 = __significant figures 2 2

11. Rule #4 • Trailing (after) zeros are only significant if there is a decimal place in the number • 202.00 = __significant figures 5

12. 4 2 • 1000. = ___ sig figs • 45000 = ___ sig figs • 450.000 = ___ sig figs • 0.004500500 = ___ sig figs 6 7

13. Practice the zero rules: 6 • 10.0098 = __sig digs • 9800 = __ sig digs • 0.009800 = ___sig digs 2 4

14. Rule #5 • Numbers obtained through counting or are defined have unlimited significant figures • 60 minutes = 1 hour • 24 people

15. Significant Figures in Calculations • An answer cannot be more precise than the least precise measurement in the calculation

16. Place value and rounding numbers 6354.2178 thousands hundreds hundreths Ten-thousandths thousandths tens ones tenths

17. Round thIS number: 9429.9385 • 1) nearest hundredth • 2) nearest ones • 3) nearest tens • 4) nearest hundreds • 5) nearest thousands

18. Rounding • Look at the digit to the right of the one you need to round. • If is is < 5 – leave it alone • If it is  5 – round up • 56.312 m = _____ (4 sig figs) • 56.31 m

19. Rounding • 0.001775 m = ___________ (2 sig figs) • 0.0018 m • 8792 m = _____________ (2 sig figs) • 8800 m

20. To Do! • Open up to page 17 • On back in top margin do this: Round these numbers to 3 sig figs: • 34678 • 0.000839967 • 120080

21. Multiplication and Division • The answer should be rounded to the same number of significant figures as the least number of significant figures in the problem

22. Examples 6.4 m2 • 4.56m x 1.4m = • 5cm x 11cm = • 0.0001800in x 19.35in = 60 cm2 0.003483 in2

23. Addition and Subtraction • Answers should be rounded to the same place value as the least number of decimal places in the calculation

24. Examples • 12.52 m + 349.0 m = • 361.52 m = 361.5 m • 74.626 m – 28.34 m = • 46.286 m = 46.29 m

25. Examples • 34 cm + 45.0 cm = • 79 cm • 46.7 mL + 52.34 mL = • 99.04 mL = 99.0 mL

26. HUMP DAY!!! 9/17 • On the bottom of pg. 17 (back) write a 3-5 sentence summary about sig figs. Make sure to answer the ESQ. • Add your “A” to your star with Sharpie. • Come get your calculator! • Edit page 18 WITHOUT CHEATING!!!

27. Trade & Grade!!!

29. Accuracy and Precision p. 199/17Obj: collect data and make measurements with accuracy and precision. ESQ: How is lab equipment used to measure precisely?

30. Accuracy • Measurement of how close a measurement comes to the actual or true value

31. Precision • Reproducibility of data • Need more than one measurement

32. Accuracy and Precision • Accurate and Precise x x x

33. Accuracy and Precision • Not Accurate but they are precise x x x

34. Accuracy and Precision • Accurate but Not Precise x x x

35. Accuracy and Precision • Not Accurate and Not Precise x x x

36. Data Sets • The data set is accurate if the values are close to the true value (literature value)

37. Data Sets • The data set is precise if all of the values are close to each other.

38. Accurate or Precise? • Several groups of students were testing different balances. They tested each balance several times using a 5.01 g weight.

39. Accurate or Precise? Mass (g) Yes Yes No Yes

40. Accurate or Precise? Mass (g) No No Yes No

41. Precision of Lab Equipment • Precision refers to the reproducibility of data • The more precise a piece of equipment, the more likely you are to get the same measurement repeatedly.

42. Precision of Lab Equipment • The more precise piece of equipment has the smallest increment change between the markings

43. Precision of Lab Equipment 30 22 21 21.0 20.20 20 20 20.0 20.00 Increment = 1 mL Increment = 0.2 mL More Precise

44. a) or More graduations – your measurements will be more precise

45. b) or More graduations – your measurements will be more precise

46. c) or More graduations – your measurements will be more precise

47. d) or More graduations – your measurements will be more precise

48. Measuring Precisely: markings = 1 mL precision = 0.1 mL 36.4 mL

49. Measuring Precisely: 11.65 cm Markings = 0.1 cm Precision = 0.01 cm

50. On the back of p. 19