Mastering Measurements: Units and Significant Figures in Science

1. Thursday, October 31, 2013 • Happy Halloween! • Standard IE1: Scientific progress is made by asking meaningful questions and conducting careful scientific experiments. • Independent Practice: • Section 3.3 Reading Packet • Question: Copy the chart into your Journal.

2. Measurements and Calculations

3. Units of Measurement • Measurements involve NUMBER and UNIT • Represent a quantity: has magnitude, size, or amount • Gram = unit of measurement • Mass = quantity

4. Units of Measurement • Scientists around the world agree on one system… • International System of Units (le Systeme International d’Unites) • SI units • Built from seven base units

5. SI Base Units

6. Units of Measurement

7. Units of Measurement • Metric Prefixes – make units easier to use • Make the unit smaller or larger • Unit = prefix + base unit • Table pg. 74

8. Mass • Measures quantity of matter • SI unit: kilogram, kg • ______ kg = _____ g • gram used for smaller masses • Weight: measure of gravitational pull

9. Length • SI unit: meter, m • Longer distances: kilometer, km • _______ km = _______ m • Shorter distances: centimeter, cm • _______ m = ________ cm

10. Volume • SI unit: m3 • A derived unit: combination of base units by multiplying or dividing • SI unit for Area: l x w = m x m = m2 • Volume: l x w x h = m x m x m = m3 • Also: liters (L), mL, dm3 and cm3 • 1 L = 1 dm3 = 1000mL = 1000 cm3

11. Derived Units

12. Scientific Notation • Put the numbers in the form a x 10n • a has one # to left of decimal • If # is bigger than 1  + exponent • If # is less than 1  - exponent

13. Scientific Notation • Review: Write in scientific notation or standard notation. a. 32,700 b. 0.0003412 c. 3.901 x 10-6 d. 4.755 x 108

14. Let’s Practice Scientific Notation Worksheet

15. 1 2 3 4 5 Significant Figures (Sig Figs) • How many numbers mean anything? • When we measure, we can (and do) always estimate between the smallest marks.

16. Significant Figures (Sig Figs) • Better marks better estimate. • Last number measured actually an estimate 1 2 3 4 5

17. Rules for Significant Figures • All nonzero digits are significant. • 457 cm has 3 sig figs • 2.5 g has 2 sig figs • Zeros between nonzero digits are significant. • 1007 kg has 4 sig figs • 1.033 g has 4 sig figs • Zeros to the left of the first nonzero digit are not significant. They are not actually measured, but are place holders. • 0.0022 g has 2 sig figs • 0.0000022 kg has 2 sig fig • Zeros at the end of a number and to the right of a decimal are significant. They are assumed to be measured numbers. • 0.002200 g has 4 sig figs • 0.20 has 2 sig figs • 7.000 has 4 sig figs • When a number ends in zero but contains no decimal place, the zeros may or may not be significant. We use scientific (aka exponential) notation to specify. • 7000 kg may have 1, 2, 3 or 4 sig figs!

18. Sig Figs • What is the smallest mark on the ruler that measures 142.15 cm? • 142 cm? • 140 cm? • Does the zero mean anything? (Is it significant?) • They needed a set of rules to decide which zeroes count.

19. Sig Figs. • 405.0 g • 4050 g • 0.450 g • 4050.05 g • 0.0500060 g

20. Sig Figs • Only measurements have sig figs. • Counted numbers are exact – infinite sig figs • A dozen is exactly 12 • Conversion factors: 100 cm = 1 m

21. Problems • 50 has only 1 significant figure • if it really has two, how can I write it? • Scientific notation • 5.0 x 101 2 sig figs • Scientific Notation shows ALL sig figs

22. Rounding Rules • Round 454.62 to four sig figs • to three sig figs • to two sig figs • to one sig fig

23. Sig Figs • How many sig figs in the following measurements? • 458 g • 4085 g • 4850 g • 0.0485 g • 0.004085 g • 40.004085 g

24. Let’s Practice Significant Figures Worksheet

25. Journal - Thursday, November 7, 2013 • Standard IE1: Scientific progress is made by asking meaningful questions and conducting careful scientific experiments. • Independent Practice: • Significant Figures Worksheet (#2) • Question: Copy the chart into your Journal. (next slide)

27. OPEN NOTE Quiz!! • When? • Blocks 1 and 3: Wednesday, November 13, 2013 • Blocks 2 and 4: Thursday, November 14, 2013 • Topics Included: • SI Units • Scientific Notation • Significant Figures • Significant Figures in Calculations • Density • Conversions

28. Vocabulary Review • Calibration: a set of graduations to indicate values or positions. • Precision: Describes the closeness, or reproducibility, of a set of measurements taken under the same conditions. • Convey: To make something known to someone. • Significant: Very important. • Intervals: A period of time between events.

29. Review:Scientific Notationand Significant Figures Worksheets

30. Calculations with Significant Figures Rules Annotate the Reading

31. Calculations with Sig Figs • 165.86 g + 4.091g - 140 g + 27.32 g • (35.6 L + 2.4 L) / 4.083 = • 2.524 x (16.408 m – 3.88 m) = Answers: 57g 9.31 L 31.62 m

32. Let’s Practice Significant Figures in Calculations WS

33. Density • Density = mass D = m volume V • Units: g/cm3 or g/mL but SI unit is kg/m3 • derived unit • Used to identify substances • Varies with temperature • As temp. increases density…

34. Density

35. Density Examples • If a metal block has a mass of 65.0 grams and a volume of 22 cubic centimeters, what is the density of the block? • D = m V • D = 65.0 g = 3.0 g/cm3 22 cm3

36. Density Examples • Aluminum has a density of 2.7 g/cm3. What volume of aluminum has a mass of 60 grams? • D = M V 20 cm3

37. Density Examples • Gold has a density of 19.3 g/cm3. A block of metal has a mass of 80 g and a volume of 12 cm3. Could this block be a piece of gold? • No, because this block has a density of 7 g/cm3s

38. Journal – Friday, November 8, 2013 • Standard: • IE1: Scientific progress is made by asking meaningful questions and conducting careful experiments. • Independent Practice: • Revise Section 3.3 Reading Packet • Calculate the Following (mind your sig figs): • (3.2 + 4.55) x 12.4 • (88.33-6.782) / 9

39. Review – Sig Figs in Calculations

40. Unit Conversions

41. Unit Conversions • Given information in one unit  need to find the equivalent in another unit • Identify what’s given • Organize plan of attack • Carry out plan WITH UNITS!!

42. Conversion factors • “A ratio of equivalent measurements.” • Start with two things that are the same. 1 m = 100 cm • Can divide by each side to come up with two ways of writing the number 1.

43. 1 m 100 cm 100 cm 100 cm Conversion factors =

44. Conversion factors 1 m = 1 100 cm

45. 1 m = 100 cm 1 m 1 m Conversion factors 1 m = 1 100 cm

46. Conversion factors 1 m = 1 100 cm = 100 cm 1 1 m

47. Conversion Factors • Unique way of writing the number 1. • Does NOT change the VALUE, it changes the UNITS.

48. Write the conversion factors for the following • kilograms to grams • feet to inches • 1 L = 1 dm3 = 1000mL = 1000 cm3

49. Method for Converting • T-Chart or Factor Label Method • Steps: • 1. Draw a Great Big “T” • 2. Put the number the problem gives you to convert to the top left of the “T”. • 3. Put the unit of that number in the bottom right part of the “T”. • 4. Write the units of what you want in the top right. • 5. Write the unit conversion factor in front of the units from Steps 3 and 4.

50. Let’s Try Some! • 323 mm = _____ nm • 3.2 miles = _____ in • 250 gallons = _____ mL • 15 days = _______ min