1. Chapter 2: Measurement and Calculations
Key concepts:
Differentiate between accuracy and precision
Apply principles of measurement and
significant figures
Identify and use the 7 base SI units
Name and apply units of measure
Perform unit conversions
Calculate density
Calculate percent error

2. A. Accuracy vs. Precision
__________ - How close you are to the correct measurement or calculation based on the standard value.
PRECISION
__________ - How close your measurements are to EACH OTHER
The density of aluminum is 2.78 g/cm3.
Bob calculates the density three times and gets 2.75, 2.79 and 2.77.
AVG: 2.77
Mary calculates the density three times and gets 4.66, 4.67, and 4.65
AVG: 4.66
Holden calculates the density three times and gets 10.25, 6.87, and 1.25
AVG: 6.12
Franz calculates the density three times and gets 2.90, 1.95, 3.44
AVG: 2.76
ACCURATE AND PRECISE
PRECISE BUT NOT ACCURATE
NIETHER ACCURATE NOR PRECISE
ACCURATE BUT NOT PRECISE

3. B. Measurement Measurement
___________ Something with magnitude, size or
amount.
Unit
________ - Compares what is measured to a
defined size.
Metric
________ - Standard system of measure using
base 10. SI
________ - The international system of measure
that uses only BASE metric units

4. B. Measurement Quantitative
___________ - Measurements having numbers or
size.
Qualitative
___________ - Measurement having subjective
descriptions
Examples:
20 ml of water
The reaction bubbles
Uma Thurman is blonde
17 g/ml
Bulldogs are #1
QUANTITATIVE
QUALITATIVE
QUALITATIVE
QUANTITATIVE
QUALITATIVE

5. C. Significant figures
Significant figures indicate the accuracy of the measuring instrument.
2.35 cm
Last digit is ESTIMATED
Not possible to estimate ; can only estimate between graduations

6. C. Significant figures Consider the following: What’s the estimate?
This ruler isn’t as accurate as the previous.

7. C. Significant figures
RULE
EXAMPLE
NO. OF SIG FIGS
All nonzero digits and zeros between those digits are significant
1 458 g
40.7 m mm
Leading zeros with decimal points are NOT significant; Ending zeros ARE significant with decimal kg m L m
Ending zeros left of the decimal point may or may not be significant. Indication needed. kg kg
1.50E4 kg
1.500E4 kg 4 3 7 1 4 6 6 2 5 3 4
Scientific notation is always in sig fig form

8. C. Significant figures ADDITION AND SUBTRACTION
Answer has as many DECIMAL POINTS as the part with the LEAST decimals.
5.44 – = – =
= =
2.83
2.8294
-13.4
-13.42
2.156
0.4
0.358

9. C. Significant figures MULTIPLICATION AND DIVISION
Answer can only contain as many SIG FIGS as the part with the LEAST sig figs
8.15 x 6 = / 0.87 =
1.2 x 1010 = / 1.50 =
48.9 50
0.29
1200
1212
11.4

10. C. Significant figures
How about this one: (not in your notes; use calc) 20

11. Scientific researchers use ONLY these units!
D. SI base units
Quantity
Unit
Abb.
Meter m
Length
Mass
Kilogram kg
Time
Second s
Temperature
Kelvin K
Amount of substance
Mole
mol
E. Current
Ampere A
Luminous intensity
candela cd
We won’t
Scientific researchers use ONLY these units!

12. D. SI Base units cont. Derived units – Made up of the base units
Quantity
SI Unit
Other Units
Area
Volume
Density
Speed
Energy
acres, cm2, ft2 m2 m3
L, gal, cm3
mi/hr, ft/s
Calorie, kWhr

13. E. Unit Conversions – metric prefixes
kilo
hecto
deca
unit
deci
centi
milli
king
hector
Doesn't
Usually
Drink
Chocolate
milk
EXAMPLES
1 000g = ________ Kg dam = _______ mm
0.23 Kg =________ dg cL = ________ HL
345 DaL = _____ Km Km = ___________ mm

14. F. Metric conversions – conversion factors
All conversions start with an EQUALITY
1 inch is the same as 2.54 cm
1 inch = 2.54 cm
Equalities are turned into conversion factors:
Notice the top and bottom are same length!

15. F. Metric conversions – conversion factors
Convert 34 inches to centimeters
2.54 cm
34 in
86.36 cm 1 in
Conversion factor goes here

16. F. Metric conversions – conversion factors
MULTI- STEP
The Bulldogs need 550 cm for a first down. How many yards is that?
Plan: cm  inch  feet  yards yd 1 in 1 ft 1
550 cm
6 yards
2.54 cm 12 in 3 ft

17. F. Metric conversions – conversion factors
A baseball is thrown 60 ft/s. How fast is this in miles/hour?
Two things to convert. Do one at a time.
1. ft  miles
2. s  min  hours 1 mi 60 s 60
min
40.91 mi/hr
5280 ft 1
min 1 hr

18. F. Metric conversions – powered units
Misconception: 1 m = 100 cm but
1m3 ≠ 100 cm3
So, 100x100x100 = 1,000,000 cm3
1 m3 cube
1 m
100 cm
If the unit is cubed, you cube the numbers too
1 m
(1 m)3 = (100 cm)3
100 cm
1 m
1 m3 = 1,000,000 cm3
100 cm

19. F. Metric conversions – Volumes
1 ml = 1 cm3
Critical equality:
How many liters of fuel does a 300 m3 tank hold? 1
1,000,000
cm3 1 ml L
300 m3
300,000 L 1 1 ml m3
cm3
1,000
Or you could do King Hector

20. F. Metric conversions - Temperature
180 Fo = ? K
Thou shalt use:
Work:

21. G. Density
Measure of how tightly packed matter is.
More dense

22. Floating Boat on SF6

23. Inhaling SF6

24. G. Density, cont. Units: When measuring LxWxH When measuring
Volume w/ cylinder

25. G. Density, cont.
A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid?
Given:
Work:
D = 0.87 g/mL
V = ?
M = 25 g

26. H. Percent Error %E = Percent error Va = Accepted value
Ve = Experimental value
Example:
A student measures the density of a solid as 3.42 g/cc. The solid really has a density of 3.76 g/cc. Calculate the percent error. cc = cubic centimeter
Va = 3.76 g/cc Ve = 3.42 g/cc

27. Watch parentheses here!!!
H. Percent Error, cont
Given:
Work:
Va = 3.76 g/cc Ve = 3.42 g/cc
Watch parentheses here!!!
%E =
%E = 9.04% (sig figs)
You can ignore negative signs. A positive percent means the accepted value is higher than your value. A negative means it’s lower.