1. 2.b Using Scientific Measurements

2. Accuracy vs. Precision
Accuracy- closeness of measurement to correct or accepted value
Precision- closeness of a set of measurements (repeatability)

3. Accuracy vs. Precision

4. Percent Error Percent Error: Measures the accuracy of an experiment
Can have + or – value

5. Example
Measured density from lab experiment is 1.40 g/mL. The correct density is 1.36 g/mL.
Find the percent error.

6. Significant Figures
All certain digits plus one estimated digit

7. Determining Number of Sig Figs
All non-zero numbers are sig figs
Zeros depend on location in number:
LEADING zeros never count
EMBEDDED zeros always count
TRAILING zeros only count if
there is a point.

8. Location of Zeros EMBEDDED: between non-zero numbers
All are sig figs
LEADING: at front of all non-zero numbers
None are sig figs
TRAILING: at the end of non-zero numbers
If there is a decimal, all are sig figs
If there is not, none are sig figs

9. Practice – how many sig figs?

10. Rounding Need to use rounding to write a calculation correctly
Calculator gives you lots of insignificant figures and you must round to the right place
When rounding, look at the digit after the one you can keep
Greater than or equal to 5, round up
Less than 5, keep the same

11. Examples make the following have 3 sig figs
     

12. Using Sig Figs in Calculations
Adding/Subtracting:
end with the least number of decimal places

13. Using Sig Figs in Calculations
Adding/Subtracting:
end with the least number of decimal places

14. Using Sig Figs in Calculations
Multiplying/Dividing:
end with the least number of sig figs

15. Using Sig Figs in Calculations
Multiplying/Dividing:
end with the least number of sig figs