1. NOTES: 3.1, part 2 - Significant Figures

2. Significant Figures:
The “sig figs” in a measurement include all of the digits that are known, plus a last digit that is estimated
The # of sig figs in a measurement depends on the precision of the instrument being used
How do we determine which digits are significant?

3. THE “RULES” FOR
SIG FIGS!!

4. 1) All non-zero numbers are significant.
EXAMPLES:
672 -
34 -
1,245 -
24,346 -

5. 1) All non-zero numbers are significant.
EXAMPLES:
sig figs
sig figs
1, sig figs
24, sig figs

6. 2) Zeroes between two non zero numbers are significant.
EXAMPLES:
202 -
1,305 -
10,001 -
3,002 -
62,004 -

7. 2) Zeroes between two non zero numbers are significant.
EXAMPLES:
sig figs
sig figs
1, sig figs
10, sig figs
3, sig figs
62, sig figs

8. 3) “Leading” zeroes are not significant (just placeholders)
EXAMPLES:

9. 3) “Leading” zeroes are not significant (just placeholders)
EXAMPLES:
sig figs
sig figs
sig figs
sig figs
sig figs

10. 4) Final or trailing zeroes are not
4) Final or trailing zeroes are not significant UNLESS there is a decimal point in the number.
EXAMPLES:
12, 5,

11. 4) Final or trailing zeroes are not
4) Final or trailing zeroes are not significant UNLESS there is a decimal point in the number.
EXAMPLES:
sig figs
sig figs
12, sig figs
sig figs
5, sig figs
sig figs
sig figs

12. 5) Powers of ten are not significant
EXAMPLES:
1.50 X
8.890 x
7.0 x x
6.35 x

13. 5) Powers of ten are not significant
EXAMPLES:
1.50 X sig figs
8.890 x sig figs
7.0 x sig figs
x sig figs
6.35 x sig figs

14. PRACTICE: Determine how many significant figures are in each of the following measurements
47,900 mm ___________
7,000,000,001 miles ___________
8.07 Hz ___________

15. PRACTICE: Determine how many significant figures are in each of the following measurements5
L ___________
m ___________
g ___________
47,900 mm ___________
7,000,000,001 miles ___________
8.07 Hz ___________ 5 5 3 10 3

16. Sig Figs in Calculations:
Find the area of a floor that measures
7.7 meters by 5.4 meters:
AREA =

17. Sig Figs in Calculations:
Find the area of a floor that measures
7.7 meters by 5.4 meters:
AREA = m2

18. But wait!...
The calculated answer has 4 sig figs, but each measurement used in the calculation only had 2!
The calculated area cannot be more precise than the measured values used to obtain it!
SO…we “round” the answer to the appropriate # of sig figs

19. ROUNDING:
After you have determined how many sig figs the answer can have, round to that many digits:
If the last significant digit is less than 5: leave the last sig fig as is;
If the last significant digit is 5 or greater: round up!

20. Practice Problems: How many sig figs in each of the following?
1) 123 meters -
2) 40,506 meters -
3) x 104 m -
4) m -
5) 98,000 m -

21. Practice Problems: How many sig figs in each of the following?
1) 123 meters - 3 sig figs
2) 40,506 meters - 5 sig figs
3) x 104 m - 5 sig figs
4) m - 4 sig figs
5) 98,000 m - 2 sig figs

22. 1) 366.2 L ___________ 2) 9,047,022 mg ___________
More practice…Round the following measurements off so that they each contain 3 significant figures.
1) L ___________
2) 9,047,022 mg ___________
3) g ___________
4) J ___________

23. More practice…Round the following measurements off so that they each contain 3 significant figures.
2) 9,047,022 mg ___________
3) g ___________
4) J ___________
366 L
9,050,000 mg
12.8 g
1.00 x 103 J
Notice this one must be in scientific notation to have 3 sig. figs.

24. NOTES: 3.1, part 2 – Operations With Significant Figures!!

25. ADDITION AND SUBTRACTION
First add or subtract, then round the answer to the last decimal place they have in common.
= = = =

26. ADDITION AND SUBTRACTION
First add or subtract, then round the answer to the last decimal place they have in common.
= = = = 1.082

27. Example: = =

28. Example: =
= 255.5
The answer is expressed as since 46.0 has only one decimal place.

29. Examples:
a b
= = = =
c d
- 0.77

30. Examples:
a b
= = = = 2.60
c d
- 0.77
= = = = 10.3

31. MULTIPLICATION AND DIVISION
Multiply or divide first, then round the answer to the same number of sig figs as the smallest number you started with.
1.311 x = =
6.884 / 2 = =

32. MULTIPLICATION AND DIVISION
Multiply or divide first, then round the answer to the same number of sig figs as the smallest number you started with.
1.311 x = = 2.88
6.884 / 2 = = 3

33. Example:
23.0 x 432 x 19 = =

34. Example:
23.0 x 432 x 19 = 188,784
= 190,000
The answer is expressed as 190,000 or 1.9 x 105 since 19 has only two sig. figs.

35. Examples:
a x =
b x =
c / =
d / =
e x 760 x =
723 x 273

36. Examples:
a x =
b x = 21
c / = 61.4
d / = 0.17
e x 760 x = 7.3
723 x 273

37. Perform the following calculations
Perform the following calculations. Round your answers to the proper # of sig. figs.
1) m / 3.21 s = ___________
2) g g g = ___________
3) 5.67 m x m = ___________
4) (5.83 m / 2.67 s) / 2.1 s = ___________
5) V x 6.0 = ___________
11.4 m/s
97.6 g
76.2 m2
1.0 m/s2
56 V
From now on, we will round all our answers to the correct # of significant figures.