1. Units of Measurement and Accuracy vs. Precision
Vocabulary
qualitative
quantitative
standard
accuracy
precision
Imperial system
metric system
SI units
“Target” – 2015
James Wright

2. Measurement
A lot of science is qualitative (observations that do not involve measurement.)
Examples:
Classifying organisms
Interpreting rock strata
Understanding the Skeletal System

3. Measurement
However, a very important aspect of science is that much of it is quantitative (observations that involve measurements)
Examples:
Determining the amount of CO2 in the atmosphere
Measuring the age of the earth
Calculating the amount of energy produced by uranium

4. Standardization
In order for scientists to communicate quantitative measurements, there must be standardized units (units that are agreed upon between scientists.)

5. Imperial (or English or Standard) System
Imperial units are the units we use most of the time here in the US. What are some examples? Length: ft, mi, yd, in, fathoms, furlongs, rods, etc. Mass: lb, oz, ton, dram, pennyweight, grain, etc. Volume: gal, pt, qt, cp, fl.oz., tsp, tbls, gill, peck, bushel, etc.

6. Imperial (or English or Standard) System
To convert between these units require conversion factors. For instance: 1 foot = _____ inches 1 gallon = _____ quarts 1 min = _____sec 1 mile = _____ feet 12 4 60
5280

7. Imperial (or English or Standard) System
More conversion factors (and this is just for volume!)

8. Imperial (or English or Standard) System
Even though the units are standardized, the complicated and inconsistent nature of the Imperial System is why only 3 countries out of 192 in the world use it.
Countries that use the Imperial system:
The United States
Liberia
Myanmar (Burma)

9. SI (International System)
All 189 other countries use the more consistent and logical SI units. They were adopted in 1960 by the General Conference of Weights and Measures and are founded on some base units: length: meter (m) mass: kilogram (kg) time: seconds (s) and some others we won’t cover right now

10. SI (International System)
What are some other SI units? length: m, km, cm, mm, etc. mass: kg, g, cg, mg, etc. time: s, ms, ks, cs, etc. volume: L, mL, kL, cL, etc.

11. SI (International System)
What are some other SI units? length: m, km, cm, mm, etc. mass: kg, g, cg, mg, etc. time: s, ms, ks, cs, etc. volume: L, mL, kL, cL, etc.
Notice that each type of measurement can have the same prefixes: kilo, centi, milli, etc.

12. SI (International System)
That’s what makes the SI units so appealing. 1 meter = 1000 millimeters 1 gram = 1000 milligrams 1 liter = 1000 milliliters 1 second = 1000 milliseconds The prefixes are consistent no matter what measurement you are making and all conversions are based on factors of 10.

13. SI Prefixes

14. However these are the only ones you will need to know.
SI Prefixes
However these are the only ones you will need to know.

15. When making measurements
Scientists don’t just need to know about units. They need to use them correctly and make accurate and precise measurements.

16. Imagine a Dart Board
If you were to throw a dart at the dart board, what you consider an accurate throw?

17. Which of these darts would you consider accurate?
Imagine a Dart Board
Which of these darts would you consider accurate? 2 1 3

18. Accuracy: the closeness of a measured value to an accepted value.
Imagine a Dart Board
#1 is accurate.
Accuracy: the closeness of a measured value to an accepted value. 1

19. Imagine a Dart Board
Because the center of the board is the accepted value for success, dart #1 is accurate. 1

20. Imagine some boiling water
If you read the thermometer and recorded a value of 102o, is your reading accurate? Why or why not?
It would not be accurate because the boiling point of water is 100oC at sea level and lower at higher elevations.

21. Now let’s talk about precision
Precision has to do with how closely multiple measured values agree with each other.

22. Imagine a dart board
Would you say that the three darts on the dart board are precise?

23. Imagine a dart board
No, they are not precise because they are not close to one another. They are inconsistent.

24. Comment on the accuracy and precision of the following darts
They are not accurate or precise.

25. Comment on the accuracy and precision of the following darts
They are both accurate and precise.

26. Comment on the accuracy and precision of the following darts
They are precise but not accurate.

27. Comment on the accuracy and precision of the following darts
The average is accurate (perhaps) but they are not precise.

28. Back to the water
Three students each perform three trials to find the boiling point of water at sea level. Their data is shown below.
Trial 1
Trial 2
Trial 3
Student 1
99o
100o
Student 2
94o
Student 3
93o
98o
95o

29. Back to the water Which student was both accurate and precise?
Trial 1
Trial 2
Trial 3
Student 1
99o
100o
Student 2
94o
Student 3
93o
98o
95o

30. Back to the water
Which student performed a good experiment but probably had a faulty thermometer?
Student #2
Trial 1
Trial 2
Trial 3
Student 1
99o
100o
Student 2
94o
Student 3
93o
98o
95o

31. Back to the water
Which student probably had multiple variables in his lab between trials?
Student #3
Trial 1
Trial 2
Trial 3
Student 1
99o
100o
Student 2
94o
Student 3
93o
98o
95o