1. Accuracy and Precision
Why do we bother with significant figures, anyway?

2. Accuracy
Extent to which a reported measurement approaches the true value of the quantity measured
Accuracy is affected by error:
Method error occurs due to the method used.
Instrument error is due to poorly calibrated or damaged instruments
Human error includes mistakes in reading or recording measurements.

3. Precision Degree of exactness or refinement in a measurement.
Precision can be affected by:
Limitations of the instrument.
Estimation skill of the person taking the measurement.
The degree of precision in a measurement is indicated by the place value of the last measureable digit.

4. Significant Figures (Digits)
The certainty of any measurement is communicated by the number of significant figures in the measurement.
In a measured or calculated value, significant figures are the digits that are known to be certain.
More digits there are, the more certain you are about the measurement.

5. How Many Significant Figures?
Rule: All non-zero digits are significant
245 m
3 sig figs

6. How Many Significant Figures?
Rule: zeros between non-zero digits are significant
1074 kg
4 sig figs

7. How Many Significant Figures?
Rule: Zeros to the left of the first non-zero digit are NOT significant. s
3 sig figs

8. How Many Significant Figures?
Rule: Zeros between non-zero digits are significant. s
6 sig figs

9. How Many Significant Figures?
Rule: Zeros at the end of a measurement that are to the right of the decimal point are significant. m
6 sig figs

10. How Many Significant Figures?
Rule: Zeros at the end of a measurement are NOT significant UNLESS you know that they were measured OR the decimal point makes them significant. m
3 sig figs

11. How Many Significant Figures?
6 sig figs
Rule: Zeros at the end of a measurement are NOT significant UNLESS you know that they were measured OR the decimal point makes them significant.

12. How Many Significant Figures?
RULE: Counted quantities and quantities that have no uncertainty do not involve significant figures.
20 students
 Sig figs

13. How Many Significant Figures?
RULE: For addition and subtraction, the answer has the same precision as the measurement with the LEAST precision (decimal places).
375.4 m m = ?
Answer = m

14. How Many Significant Figures?
RULE: For multiplication and division, the answer has the same number of significant figures as the measurement with the FEWEST significant figures.
(20.0 m)(3.0 m) = ?
Answer = 60. m or 6.0 x 10 1 m

15. Homework
Read page 258
Page 257 #7, 11-15