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Significant (Measured) Digits

Significant (Measured) Digits. Measuring with Precision. Significant Digits (sd). Defn: Those numbers that result from directly measuring an object. It shows the precision of the measurement. Units must be included (no units no sd)

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Significant (Measured) Digits

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  1. Significant (Measured) Digits Measuring with Precision

  2. Significant Digits (sd) Defn: Those numbers that result from directly measuring an object. It shows the precision of the measurement. Units must be included (no units no sd) The precision of the measurement depends upon the measuring instrument Use the following PRIORITIZED list to determine the number of sd’s in a measurement, calculation, or conversion

  3. Rule 1: All nonzero digits are significant (they were measured) • Samples • a. 234 m • b. 1678 cm • c. 0.23 g • SD’s and precision • a. 3 sd to the m • b. 4 sd to the cm • c. 2 sd to the cg

  4. Rule 2: All zeros between nonzero (or significant) digits are significant Translation: In between 0s must be measured • Samples • a. 202 mm • b. 1003 cm • c. 0.200105 m • SD’s and precision • a. 3 sd to the mm • b. 4 sd to the cm • c. 6 sd to the mm

  5. Rule 3: Zeros to the right of a nonzero digit but to the left of an understood decimal are NOT significant unless otherwise indicated. Translation: 0s at the end of a whole number are NOT measured unless marked. • a. 200 cm • b. 109,000 m • c. 1,000,000 mm • d. 200 cm • e. 200 cm • a. 1 sd to the m • b. 3 sd to the km • c. 1 sd to the km • d. 3 sd to the cm • e. 2 sd to the dm (a bar over a zero indicates the last measured zero)

  6. Rule 4: All zeros to the right of a decimal point but to the left of a nonzero digit are NOT significant. Translation: 0s in front of a number less than 1 are NOT measured. • Samples • a. 0.0032 m • b. 0.01294 g • c. 0.00000002 L • SD’s and precision • a. 2 sd to the .1 mm • b. 4 sd to the .01 mg • c. 1 sd to the .01 mL

  7. Rule 5: All zeros to the right of a decimal point and following a nonzero digit are significant Translation: 0s at the end of a decimal number are measured. • Samples • a. 20.00 g • b. 0.07080 mm • c. 1.0400 cm • d. 45.00 • SD’s and precision • a. 4 sd to the cg • b. 4 sd to the .01 mm • c. 5 sd to the mm • d. 0 sd

  8. How to use this information when converting/evaluating measures Examine the number & go through rules IN ORDER Rule 1 - underline any nonzero digits Rule 2 - underline any zeros between these Rule 3 - place an ‘n’ under the zeros at the end of a whole number (after any overlined 0s) Rule 4 - place an ‘n’ under zeros in front of a number less than one Rule 5 - underline zeros at the end of a decimal number Count the number of underlined digits = # sd

  9. How to use SD rules when multiplying/dividing • Rule: Your calculation (answer) must have the same precision as the LEAST precise original measurement • Find the number of significant digits in each of the starting numbers and note the lowest number of significant digits • ex. 2.40 cm x 3 cm (lowest # of sd is 1) • Calculate your answer • Round the answer to the lowest # of sd found in #1 • 2.40 cm x 3 cm = (7.2 cm2) = 7 cm2

  10. Significant Figures

  11. Significant Figures • All measurements are inaccurate • Precision of measuring device • Human error • Faulty technique

  12. Significant Figures • Measurements need to convey precision • Must include degree of uncertainty • Sig Figs tell us

  13. Significant Figures

  14. Significant Figures • Significant figures in a measurement include • all of the digits that are known precisely • plus one last digit that is estimated.

  15. Significant Figures 2. Non-zero digits are always significant. 103.230002

  16. Significant Figures 3. All final zeros after the decimal point are significant. 12.740 0.0420

  17. Significant Figures 4. Zeros between two other significant digits are always significant. 10.0 2004 6.000

  18. Significant Figures 5. Zeros used only for spacing the decimal point are not significant. 100 0.00000233

  19. Killing Babies • Always put a 0 in front of a decimal point • 0.247  • 0.0042  • .873 

  20. Significant Figures

  21. Significant Figures

  22. Significant Figures

  23. Significant Figures 6. If you add or subtract, the answer is rounded to the same number of decimal places as the measurement with the least number of decimal places.

  24. Significant Figures 7. If you multiply or divide two numbers, the answer is rounded off to the number of significant figures in the least precise term used in the calculation (i.e. the number with the fewest sig figs).

  25. Calculations

  26. Calculations

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