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Understanding Precision and Accuracy in Measurements

Learn about precision and accuracy in measurements, significant figures, and scientific notation. Discover the rules for determining significant figures and how to apply them. Master the concepts to enhance your math skills.

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Understanding Precision and Accuracy in Measurements

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  1. Journal #1 8/9/10 • Solve for x if • Solve for x if

  2. Math and Graphing Notes Chapter 1

  3. Precision • The precision of a number describes the degree of exactness of the measurement. • Ex. A beaker of water is placed on a triple beam balance and is measured to have a mass of 421.5 grams. The same beaker is placed on an electronic balance and the mass is given as 421.5211 grams. Both numbers are correct, but the second number is more precise.

  4. Accuracy • For a measurement to be accurate, the value must be very close to the “real” value. • Ex. The teacher has already measured the mass of a wooden block to be 11.2 grams. If a student were to measure the same block and return a mass of 11.3 grams, we would say that the student had a very accurate measurement.

  5. Accuracy vs. Precision

  6. Significant Figures • All measurements that are made are subject to some uncertainty. • Some scales that you weigh objects on might read to 1 decimal place while others might be more precise and measure to 3 decimal places • When doing math with measurements, numbers cannot become more precise.

  7. Determining Sig Figs • When given any number, there are rules that can be followed to determine how many digits within that number are “precise” digits, aka Sig Figs.

  8. Determining Sig Figs • Let’s look a few examples: • 1492 • 101 • 200 • 0.005 • 0.750 • 102.070

  9. Determining Sig Figs • We will work through all 5 rules • The first rule is the easiest… • All numbers that are non-zero numbers are ALWAYS sig figs. • When you first start counting Sig Figs, you may want to underline digits that are significant to help you.

  10. Determining Sig Figs • Underline the non-zero digits: • 1492 (all of these are sig figs) • 101 (both of the 1’s) • 200 (only the 2) • 0.005 (only the 5) • 0.750 (only the 7 and the 5) • 102.070 (only the 1, 2, and 7)

  11. Determining Sig Figs • The only numbers remaining now are zeros. The last 4 rules are called the zero rules. • Zero Rule #1 is easier to remember as the “sandwich rule”. • If a zero is anywhere between two sig figs, it is also a sig fig.

  12. Determining Sig Figs • Underline the sandwich zeros: • 1492 • 101 (yes) • 200 (no sandwich) • 0.005 (no sandwich) • 0.750 (no sandwich) • 102.070 (only the first and second 0)

  13. Determining Sig Figs • Zero Rule #2 is also called the “trailing zero” rule • Zeros that fall behind a sig fig but are in front of the understood decimal point are NOTsig figs.

  14. Determining Sig Figs • Look for any trailing zeros: • 1492 • 101 • 200 (yes… both trail, so not sig figs) • 0.005 (no, but the zero in front of the decimal is obviously not a sig fig) • 0.750 (no) • 102.070 (no)

  15. Determining Sig Figs • Zero Rule #3 is also called the “leading zero” rule • Zeros that fall behind the decimal but are in front of a sig fig are NOTsig figs.

  16. Determining Sig Figs • Look for any leading zeros: • 1492 • 101 • 200 • 0.005 (yes, the two zeros in front of the 5 are leading zeros and are not sig figs) • 0.750 (no) • 102.070 (no)

  17. Determining Sig Figs • Zero Rule #4 is also called the “precision” rule • Zeros that fall behind the decimal AND are behind a sig fig are sig figs.

  18. Determining Sig Figs • Underline any precision zeros: • 1492 • 101 • 200 • 0.005 • 0.750 (yes, the last 0) • 102.070 (yes, the last 0)

  19. Determining Sig Figs • Final Count: • 1492 (4 sig figs) • 101 (3 sig figs) • 200 (1 sig fig) • 0.005 (1 sig fig) • 0.750 (3 sig figs) • 102.070 (6 sig figs)

  20. Things to remember… • Once you call a number a sig fig, you can’t undo it by a later rule. • Always follow the rules in order as you determine sig figs. • There may be times where you have recheck the sandwich rule at the end. • Example: 50.00

  21. Journal #2 8/11/10 • Determine the number of sig figs: • 10.70 • 10200 • 0.033 • 2.000 • 1350 • 0.0050

  22. Journal #2 8/11/10 • Determine the number of sig figs: • 10.70 (sandwich and precision) • 10200 (sandwich) • 0.033 (leading zeros don’t count) • 2.000 (precision) • 1350 (trailing zero doesn’t count) • 0.0050 (precision zero only)

  23. Scientific Notation • Many times in science we have to use very large numbers or very small numbers. In these times, it makes more sense to use a special notation rather than writing a number like 9,000,000,000,000 (same as 9x1012) • When using Scientific Notation, you mustknow how to count sig figs.

  24. Scientific Notation • Luckily, most calculators can do this for you. But… in the event that you forget your calculator, everyone should know how to do this by hand. • After we review the “old-fashioned way”, I will demonstrate how to do this on the calculator.

  25. Scientific Notation • Please copy down these 3 example numbers. • 2603000 • 0.0000484 • 300000000 • Please follow the rules and underline the sig figs in each number.

  26. Scientific Notation • Check your sig figs: • 2603000 • 0.0000484 • 300000000 • Next, locate the decimal point in each number. If you don’t see a decimal point, it is understood to be at the far right (draw one in).

  27. Scientific Notation • Check your decimal points: • 2603000. • 0.0000484 • 300000000. • To convert, you simply count the number of “places” that you will move the decimal until it lands behind the sig fig farthest to the left.

  28. Scientific Notation • Check your decimal points: • 2603000. (6 places) • 0.0000484 (5 places) • 300000000. (8 places)

  29. Scientific Notation • The number of places will become the exponent on the power of ten (10n) • If you move left the power is positive (think big), and if you move right the power is negative (think small).

  30. Scientific Notation • All you have to do now is write the number (dropping all digits but the sig figs) and add on the power of ten. • For example A • 2603000. becomes 2.603 x 106 • Try doing the other two

  31. Scientific Notation • Check your answers: • 0.0000484 = 4.84 x 10-5 • 300000000. = 3 x 108 Remember: This was an understood decimal point

  32. Scientific Notation • Now, the easy way… • Find a button on your calculator with the letters SCI (may be above a button or by pressing “mode”) • Select SCI to place your calculator in Scientific mode • Type any of our three examples and press enter.

  33. Scientific Notation • So a calculator can tell you the scientific notation for any number… GREAT! • But what if I give you a question where the numbers are already in scientific notation and you have to use them mathematically… • How do you type them on the calculator?

  34. Scientific Notation • Copy down the following question: • (3.00 x 108) x (4.80 x 102) = ? • Before we go on, locate one of the following buttons on your calculator: EE, x10n, or EXP

  35. Scientific Notation EE, x10n, or EXP • These buttons allow you to enter a number that is already in scientific notation. • To enter the first number, press this: ( 3.00 EE 8 ) • You will probably see that the calculator screen only shows one E… that’s ok… don’t press it twice!

  36. Scientific Notation EE, x10n, or EXP • To continue the problem, press this: x (4.80 EE 2) = • Your calculator will generate the answer for you and most likely give that answer in scientific notation. • Please wait for everyone to catch up.

  37. Scientific Notation • Check your answer: • (3.00x108) x (4.80x102) =? • 1.44x1011 • Raise your hand if you didn’t get this answer.

  38. About your final answer… • Now comes the reason we have done all of this… • In science, you are never allowed to give a more precise answer than the measurements you started with. • The rule is that you must have the same number of sig figs in your answer as the LEAST amount in any number used in the problem.

  39. About your final answer… • In this case, 1.44x1011, has the same number of sig figs as both of the beginning numbers (3). So no extra work is required. • If you were to end up with less sig figs than required, you would simply add on precision zeros. • If you were to end up with more sig figs than required, you would round the number.

  40. Examples: • Make each of the following numbers have 3 sig figs (use rounding or precision zeros): • 2.758 x 10-8 • 5.1 x 104 • Check with your neighbor

  41. Examples: • Check your answers: • 2.758 x 10-8 rounds up to 2.76 x 10-8 • 5.1 x 104 adds a precision zero to become 5.10 x 104

  42. Journal #3 8/12/10 • Calculate the answer, remember to use the correct sig figs in your answer:

  43. Journal #3 8/12/10 • Your answer must only have 2 sig figs

  44. Dimensional Analysis • In the metric system, prefixes are used on units to indicate the power of 10. You are expected to be able to convert between these without hesitation. (blanks are important, but you don’t need to know what goes there) G _ _ M _ _ k h da _ d c m _ _ μ _ _ n

  45. G _ _ M _ _ k h da _ d c m _ _ μ _ _ n

  46. Dimensional Analysis • Convert the following numbers: • 3.75km = ______ m • 0.003m = _______ mm • 750g = _______ kg • 2490mL = ______ L • 0.0890kg = ______ cg (in sci. not.)

  47. Dimensional Analysis • Convert the following numbers: • 3.75km = 3750m (3 spaces right) • 0.003m = 3mm (3 spaces right) • 750g = 0.75kg (3 spaces left) • 2490mL = 2.49L (3 spaces left) • 0.0890kg = 8.90x103cg (5 spaces right, but 3 sig figs)

  48. Journal #4 8/13/10 • Describe how confident you are about the different parts of the quiz. • After the quiz, open your journal and write about how you feel you did.

  49. Journal #6 8/19/09 • About how far had the ball fallen at 0.8s? • How long did it take for the ball to fall 12m? ? ?

  50. Parts of a line graph: • Title • Axis Labels • Number Scale • Data Points • Line • Legend/Key

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