1. Using Scientific Measurements

2. Accuracy and Precision Accuracy –How close a measurement is to the true or accepted value Determined by calculating % Error % Error = Experimental Value – Accepted Value x 100 Accepted Value

3. Accuracy and Precision Precision – how close the measurements are to each other –Repeatability –Do you get the same number every time you do the experiment?

4. Dartboard Analogy Accurate & Precise Accurate, Not Precise Precise, Not Accurate Neither

5. Uncertainty… Always present in measurement because you always end up estimating –S–Something you cannot escape! –S–Should be listed as a + value –E–Example: 50.01 g + 0.01 g

6. Significant Figures Sig Figs –Help indicate precision of measurements –Used so scientists can all speak the same mathematical language

7. Significant Figures General Rules –Record all digits that are absolutely certain –Record ONE last estimated number “Read between the lines” –Zeroes are tricky and can be either: Placeholders Sig figs

8. Significant Figures Rules All non-zero digits are sig figs –235.67 5 sig figs –45.6 3 sig figs –14567.8 6 sig figs

9. Significant Figures Rules Zeroes between non-zero digits are significant (if we know the digits on both sides, we know the ones in between) 105 –3 sf’s 3000005 –7 sf’s 0.3009 –4 sf’s 15.004 –5 sf’s

10. Significant Figures Rules Zeroes which locate the decimal are non- significant placeholders They tell you how big or how small the number is You can’t be lazy and leave them off

11. Significant Figures Rules Examples: –1000 1 sf –7300 2 sf’s –0.092 2 sf’s –0.0001 1 sf –85170 4 sf’s

12. Significant Figures Rules Zeroes to the right of a DECIMAL are sig figs You would leave them off if you were being lazy The only reason they’re there is because they were measured!

13. Significant Figures Rules Examples: 32.0 –3 sf’s 0.00010 –2 sf’s 0.53000 –5 sf’s

14. Significant Figures Rules Counted numbers have infinite sig figs There is no lack of precision when counting If you have 3 pencils, you have 3 pencils. Exactly. No more, no less. Each time you count, you’ll get the same number.

15. Calculations with Sig Figs Addition and Subtraction –Your answer should have the same number of DECIMAL PLACES as the quantity with the least number of decimal places –3.50 – 1.5 = 2.0 –4.600 – 2 2.6  3 Follow rounding rules!

16. Calculations with Sig Figs Multiplication and Division –Your answer should have the same number of SIG FIGS as the quantity with the least sig figs –4.0 / 2 2 –2.50 x 2.000 5.00 Follow proper rounding rules!