1. 2.5 Reading Measurements and Experimental Uncertainty (Part 1)

2. 2.5 Part 1 Learning Outcomes
Learn how to find and report the uncertainty associated with each measurement
Determine if a measurement is accurate and/or precise
Determine certain and uncertain digits in a measurement
Determining experimental uncertainty

3. Part 1 Vocabulary Counting Exact or Definite number Uncertainty
Significant figure
Accurate
Precise
Certain verses uncertain digits
Experimental uncertainty

4. 2.5 Part 1 Summary Notes (Reading Measurements and Experimental Uncertainty):
Sample Question 1: Write the following measurement and its uncertainties in the correct form- a balance gives the measurement of 51.32g with an uncertainty of 0.01g
/- 0.01g
Sample Question 2: The correct volume of a metal is cm3
A several readings of would be precise but NOT accurate
A reading of 18 would be accurate but NOT precise

5. Summary Notes: counting a small # of objects = exact or definite
measuring mass, time, volume, length = measured and are never exact
All measurements have uncertainty associated with them
Significant figure is a measured or MEANINGFUL digit (see SWB page 27 for examples)

6. Accurate and Precise:
Accurate= measure that is close to the correct or accepted value
Precise= reproducible measurement, more significant digits/more decimal places

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

8. Can something be precise but not accurate (or vice versa)?
YES!!!
if precise, but not accurate there is a systematic error or bias
Ex. you get the same wrong answer over and over
if accurate but not precise, experimenter is being inconsistent

9. For example: Assume the CORRECT measurement of a pencil is 27.3200 cm.

10. LOTS of Sig Figs

11. Uncertainty (not just a feeling)

13. We would write this as….
42.6 +/- 0.1 mL

14. Another Example:
What number would this be?

15. More Examples:
6.214
6.372

16. Uncertainty in Measurements:
The uncertainty is always in the last digit (the one that was estimated)
This can be expressed as part of the number
Ex mL
uncertainty term

17. Uncertainty in Measurements:
The uncertainty is always in the last digit (the one that was estimated)
This can be expressed as part of the number
Ex mL
 Range = 42.6 to 42.8mL

18. Assume that a measured temperature is 39
Assume that a measured temperature is 39.6ºC and the uncertainty is ± 0.1ºC. We write it as:
The RANGE for the above measurement is from
39.5 – 39.7ºC.

19. Practice task(s) to learn these new skills
1. Exercise page 29 (Accurate and precise, certain digits and measurement/counting)
2. Exercise #48 page 32, #49 page 33 and #50 page 34 (practice reading scales)
3. Exercise # 51 and #52 page 35 and finally Exercise # 53 and 54 page 36