1. Science, Measurements, Uncertainty and Error
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Science, Measurement, Uncertainty and Error

2. Conversion of Units

3. Conversion Factor A conversion factor is a ratio between two units:
The conversion factor can be written with either value on top, just set it up so that things cancel out!

4. Example 27.777...m/s How fast is 100 km/h in m/s? Write what you have…
multiply by conversion factor(s)…
m/s
do the math…
multiply the tops,
multiply the bottoms,
then divide these 2 #’s

5. Example How fast is 50mph in m/s? Write what you have…
multiply by conversion factor(s)…
do the math…
multiply the tops,
multiply the bottoms,
then divide these 2 #’s
m/s

6. Uncertainty in Measurement and Significant Figures

7. Precision
The darts are all close to one another. They may or may not be close to the intended target.

8. Accuracy Dart is right on target. (The value
is close to what it should be.)

9. Precision and Accuracy in Measurements
How close are the measurements to the true value.
Precision
How reproducible are measurements?

10. Dartboard analogy
Imagine a person throwing darts, trying to hit the bulls-eye.
Not accurate
Not precise
Accurate
Not precise
Not accurate
Precise
Accurate
Precise

11. Scientific Data
Scientists always want the most precise and accurate experimental data.
The precision and accuracy are limited by the instrumentation and data gathering techniques.

12. Dealing with Errors HOW? Identify the errors and their magnitude.
Try to reduce the magnitude of the error.
HOW?
Better instruments
Better experimental design
Collect a lot of data

13. Counting Sig Fig’s – 4 Rules:
Nonzero digits are always significant
All final zeros after the decimal point are significant
Zeros between two other significant digits are always significant
Zeros used solely as placeholders are not significant

14. Counting Sig Fig’s – Sci. Notation
Use Scientific Notation…
Determine how many digits are important when writing the number in scientific notation.

15. How many significant figures?
1,460 3

16. How many significant figures?
21.76 4

17. How many significant figures?
421.03 5

18. How many significant figures?
.002 1

19. How many significant figures?
1,000.1 5

20. How many significant figures?
726.01 5

21. How many significant figures?
720 2

22. How many significant figures?
4.801 4

23. How many significant figures?
0.103 3

24. How many significant figures? 3

25. How many significant figures?
1.47 3

26. How many significant figures?
1,200 2

27. How many significant figures?
1,200,000.0 8

28. How many significant figures?
120 2

29. How many significant figures?
4.60 3

30. How do you round? Rounding is different, depending on whether you are
adding or subtracting OR
multiplying or dividing

31. Adding/Subtracting Add/Subtract first
Round according to the fewest number of Digits After the Decimal

32. Examples:
286.9
2.251
507.8

33. Multiplying/Dividing
Multiply/Divide first
Round according to the fewest number of Significant Figures

34. Examples:
12,000 92
380