1. Accuracy and Precision
Measurement
Accuracy and Precision

2. Vocab. to describe good measurements
Accuracy –
how close the measurement is to the actual value
Precision –
how well can the measurement be repeated
requires several measurements before anything can be said about it

3. Let’s use a golf anaolgy

4. Accurate? No
Precise?
Yes 10

5. Accurate?
Yes
Precise?
Yes 12

6. Accurate? No
Precise? No 13

7. Accurate?
Yes
Precise?
We cant say! 18

8. PRECISE = CONSISTENT(Repeatable)
Accuracy vs. Precision
ACCURATE = CORRECT
PRECISE = CONSISTENT(Repeatable)

9. Accuracy vs. Precision Good accuracy Good precision Poor accuracy
Scientists repeat experiments many times to increase their accuracy.
Good accuracy
Good precision
Poor accuracy
Good precision
Poor accuracy
Poor precision

10. In terms of measurement
Three students measure the width of the classroom to be m, 10.3 m and 10.4 m across.
Were they precise?
Were they accurate?

11. Measurement
Percent Error

12. Error
The difference between an experimental value and an accepted value
Error = experimental value – accepted value

13. Percent Error Tells us the accuracy of an experiment
The lower the value the more accurate!
Percent error = experimental value – accepted value x 100
accepted value

14. Practice Example
Use Student A’s density data in the table below to calculate the percent error in each trial.
Report your answers to two places after the decimal point.
The accepted value for the density is 1.59 g/cm3
Density
Error
Exp - Acc
Percent Error
Trial 1
1.54
Trial 2
1.60
Trial 3
1.57

15. Based on the Percent (%) Error Table from Mr
Based on the Percent (%) Error Table from Mr. Mayberry’s AP Chem Class, who had the most accurate results:
Keith
Mary
Trevor
Bill
Percent (%) Error
33.6 %
42.9 %
2.7 %
12.6 %