1. Scientific
Measurement

2. Scientists prefer QUANTITATIVE as there is no room for bias!
Types of measurement
Quantitative- use numbers to describe
Qualitative- use description without numbers
4 feet
extra large
Hot
100ºF
Scientists prefer QUANTITATIVE as there is no room for bias!

3. Remember…
Numbers without units are meaningless.
NO NAKED NUMBERS!!!

4. Reading a Ruler . l2. . . . I . . . . I3 . . . .I . . . . I4. . cm
What is the length of this line?

5. Reading a Ruler
. l I I I I4. . cm First digit (known) = 2 2.?? cm Second digit (known) = ? cm Third digit (estimated) between Length reported = 2.65 cm or 2.64 cm or 2.66 cm

6. How good are measurements?
Accuracy- how close the measurement
is to the true value
Precision- how well can the measurement
be reproduced

7. Let’s use a golf anaolgy

8. Accurate? No
Precise?
Yes

9. Accurate?
Yes
Precise?
Yes

10. Precise? No
Accurate? No

11. Accurate?
Yes
Precise?
We can’t say!

12. Significant figures (sig figs)
How many numbers in a measurement means something
When we measure something, we can (and do) always estimate between the smallest marks. 2 1 3 4 5

13. Significant figures (sig figs)
More marks = More precision Scientists always understand that the last number measured is actually an estimate 1 2 3 4 5

14. Go to your lab station
Note the smallest scale marks for each, and to what place you should estimate:
100 mL Grad Cyl
50 mL Grad Cyl
25 mL Grad Cyl
10 mL Grad Cyl
50 mL Buret
100 mL Buret
Electronic balance
1mL so, est.→ 0.1 mL
1mL so, est.→ 0.1 mL
0.2 mL so, est.→ 0.1 mL
0.1mL so, est.→ 0.01 mL
0.1mL so, est.→ 0.01 mL
0.2 mL so, est.→ 0.1 mL
0.01 g

15. Sig Figs (sig digs)
Since science tools aren’t precise to infinite digits, we say only certain numbers are “significant” to us.

16. Atlantic/Pacific Rule
Number
Pacific
Atlantic
If decimal is “Present” start counting from the Pacific
Side at the first “non-zero” digit and continue counting
until the number ends.
If the decimal is “Absent” start counting from the
Atlantic side at the first “non-zero” digit and continue
counting until the number ends.

17. How many sig figs in these measurements?3
#2: g
#3: g
#4: g 9

18. Which measurement has 3 sig figs?
2.013
4200
74.0
830

19. Round the following numbers to three sig figs. #1: 47. 389 47

20. Round to four sig figs.
5459
5500.
5458

21. What about this measurement?20 10 30 40 50
How many significant figures should you have? How do you write 30 with two sig figs? 30.

22. Adding and Subtracting with sig figs
Your answer when you add or subtract can not be more “significant” than your worst estimate.
Find the answer, then round to the least significant place of any measurement in the problem

23. For example 27.93 6.4 + 34.33 = Also tenths place Tenths place
(least precise
Measurement)
Find the answer first, then round to the least significant place of any measurement in the problem.

24. Practice
#1:
= 11.7
#2:
= 2.118
#3:
6.158 = 6.2

25. – 2.00 = ?
12.44
12.442
12.440
12.50

26. Multiplication and Division
Rule is different from addition and subtraction
Answer has the same number of sig figs as the least significant number in the problem
x =
= 2400
2 sig figs
3 sig figs
Can ONLY have 2 sig figs
Remember, the rules are the same for division.

27. Multiplication and Division
#1) / =
= 0.72
#2) x =
= 28
#3) / = =