1. BELLWORK 9/01/17
Complete #’s 1, 12, 22, and 34 in the new Virginia Bellwork Packet.

2. Why do we have to learn about Sig Figs?

3. Sig Figs tell you what place to round your answers to.
Your final measurement (answer) can never be more precise than your starting measurement.
To understand that idea, we will discuss accuracy vs. precision

4. Two important points in measurement
Accuracy & Precision
Two important points in measurement

5. THE BIG CONCEPT
Accuracy –indicates the closeness of the measurements to the true or accepted value.
2. Precision - The closeness of the results to others obtained in exactly the same way.

6. Accuracy vs. Precision High Accuracy High Precision High Precision
Low Accuracy

7. Master Archers

8. Can you hit the bull's-eye?
Three targets with three arrows each to shoot.
Accurate and precise
Precise but not accurate
Neither accurate nor precise
How do they compare?
Can you define accuracy vs. precision?

9. Example: Accuracy
Who is more accurate when measuring a book that has a true length of 17.0 cm?
Susan:
17.0 cm, 16.0 cm, 18.0 cm, 15.0 cm
Amy:
15.5 cm, 15.0 cm, 15.2 cm, 15.3 cm

10. Example - Precision Which set is more precise? A. 18.2 , 18.4 , 18.3
B , 18.3 , 18.8
C , 17.2 , 19.4

11. Precision and Instruments
Do all measuring devices have the same amount of precision?

13. You indicate the precision of the equipment by recording its Uncertainty
Ex: The scale on the left has an uncertainty of (+/- .1g)
Ex: The scale on the right has an uncertainty of (+/- .01g)

14. Significant Figures
In Measurements

15. Significant Figures
The numbers reported in a measurement are limited by the measuring tool.

16. How to Determine Significant Figures in a Problem
Use the following rules:

17. Rule #1 Every nonzero digit is significant in a measurement. Examples:

18. Rule #2 – Sandwiched 0’s Zeros between non-zeros are significant
Examples:
203,205 = 6
7003m = 4
40.9m = 3

19. Rule #3 – Leading 0’s
Zeros appearing in front of non-zero digits are not significant
Act as placeholders
Examples:
= 2
0. 24m =
0.453m =

20. Rule #4 – Trailing 0’s with Decimal Points
Zeros at the end of a number and to the right of a decimal point are significant.
Examples:
1.0 = 2
43.00m = 4
1.010m = 4
1.50m = 3

21. Performing Calculations with Significant Figures
Rule: When adding or subtracting measured numbers, the answer can have no more places after the decimal than the LEAST of the measured numbers.
Only count the Sig Figs that come after the decimal.

22. Adding and Subtracting
2.45cm + 1.2cm = 3.65cm,
Round off to  3.7cm
7.432cm + 2cm = 9.432
Round to  9.4cm

23. Multiplication and Division
Rule: When multiplying or dividing, the result can have no more significant figures than the least reliable measurement.
Count all of the Sig figs in the entire number.

24. Examples 75.8cm x 9.6cm = ? 56.78 cm x 2.45cm = 139.111 cm2
Round to  139cm2
75.8cm x 9.6cm = ?

25. Learning Check
State the number of significant figures in each of the following:
A m
B L
C g
D m
E. 2,080,000 bees

26. Learning Check A. Which answer(s) contain 3 significant figures?
1) ) ) 4760
B. All the zeros are significant in
1) ) ) x 103
C. 534,675 rounded to 3 significant figures is
1) ) 535, ) 5.35 x 105

27. Learning Check
In which set(s) do both numbers contain the same number of significant figures?
1) m and m
2) m and 40 m
3) m and 150,000 m