1. Page 20 UNIT 2- Measurement in Science

2. Accuracy and Precision
These notes go on page 21

3. Accuracy how close a measurement comes to the actual or true value
Think of accuracy like hitting the bullseye on a target.

4. Precision Can you reproduce the data?
Precision is getting the same measurement more than twice.
Need more than one measurement.
Think of this like hitting the same area of a target more than once.

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

6. Accuracy and Precision
Accurate and Precise x x x

7. Accuracy and Precision
Not Accurate but they are precise x x x

8. Accuracy and Precision
Accurate but Not Precise x x x

9. Accuracy and Precision
Not Accurate and Not Precise x x x

10. Precision of Lab Equipment
Precision refers to the reproducibility of data
The more precise a piece of equipment, the more likely you are to get the same measurement repeatedly.

11. Precision of Lab Equipment
When you look at a piece of equipment, first look at its graduations (markings) and try to find out what the lines mean.
The more precise piece of equipment has the smallest increment change between the markings
Usually the piece of equipment with the more graduations (lines) is the more precise.

12. Precision of Lab Equipment30 22 21
21.0
20.20 20 20
20.0
20.00
Increment = 1 mL
Increment = 0.2 mL
More Precise

13. a) or
More graduations – your measurements will be more precise

14. b) or
More graduations – your measurements will be more precise

15. c) or
More graduations – your measurements will be more precise

16. d) or
More graduations – your measurements will be more precise

17. Measuring Precisely:
36.4 mL
markings = 1 mL precision = 0.1 mL

18. Measuring Precisely:
11.65 cm
Markings = 0.1 cm Precision = 0.01 cm

19. d) or
More graduations – your measurements will be more precise

20. Data Sets
The data set is accurate if the values are close to the true value (literature value)

21. Data Sets
The data set is precise if all of the values are close to each other.

22. Accurate or Precise?
Several groups of students were testing different balances. They tested each balance several times using a 5.01 g weight.

23. Accurate or Precise? Mass (g) Yes Yes No Yes Balance Trial #1 #2 #3
4.98
5.01
5.00 B
4.05
3.98
4.00
Yes
Yes No
Yes

24. Accurate or Precise? Mass (g) No No Yes No Balance Trial #1 #2 #3
3.57
6.04
4.59 D
5.05
4.90
5.10 No No
Yes No