Friday's notes

1. Accuracy & Precision
Two important points in measurement
(We start the year with a math unit then
we will study atoms, ions, and the
periodic table.)

2. Accuracy and Precision
At the conclusion of our time
together, you should be able to:
1. Explain the difference between the accuracy
and precision
2. Give examples of accuracy and precision
This information is from Chapter 3.1

3. Accuracy
 Accuracy = the extent to which a
measured value agrees with a standard
value
Accuracy of a device must be checked
Does it read a proper accepted value?
 Beware of Parallax – the apparent shift
in position when viewed at a different
angle.

4. Graduated Cylinder –
Meniscus and Parallax

6. 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

7. Murphy's Laws
of
Science and Technology
Technology is dominated by those who manage
what they do not understand.

8. Precision
 Precision = the degree of exactness of
a measurement that is repeatedly
recorded.
 Which set is more precise?
18.2 , 18.4 , 18.35
17.9 , 18.3 , 18.85
16.8 , 17.2 , 19.44

9. Example: Precision
Who is more precise when measuring the same
17.0 cm book?
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. Accuracy vs. Precision
High Accuracy
High Precision
High Precision
Low Accuracy

11. CCaann yyoouu hhiitt tthhee bbuullll''ss--eeyyee??
TThhrreeee
ttaarrggeettss wwiitthh
tthhrreeee
aarrrroowwss eeaacchh
ttoo sshhoooott..
Both
accurate
and
precise
Precise
but not
accurate
Neither
accurate
nor
precise
HHooww ddoo
tthheeyy
ccoommppaarree??
CCaann yyoouu ddeeffiinnee aaccccuurraaccyy vvss.. pprreecciissiioonn??

12. Why Is There Uncertainty?
• Measurements are performed with instruments,
and no instrument can read to an infinite number of
decimal places
•Which of the instruments below has the greatest
uncertainty in measurement?

13. The Scientific Method
begins with
Questions about the World Around You.
Ever Wonder Why?...
Braille dots are on the keypads of drive-up
ATM's?

14. Accuracy and Precision
Let’s see if you can:
1. Explain the difference between the accuracy
and precision
2. Give examples of accuracy and precision

15. Exit Quiz: Evaluate whether the
following are precise, accurate or both.
Low Accuracy
Low Precision
Low Accuracy
High Precision
High
Accuracy
High
Precision

16. Significant Figures
In Measurements

17. Significant Figures
At the conclusion of our time
together, you should be able to:
1. Explain what significant figures are in a
measurement
2. Determine the number of significant figures
in any measurement

18. Significant Figures
The significant figures in a measurement include all
of the digits that are known, plus one last digit
that is estimated.
The numbers reported in a measurement are
limited by the measuring tool.