Making Measurements

1
Making Measurements

• Units and Conversions
• Significant Figures

2
Three Parts of a Measurement

• Magnitude
• Units
• Uncertainty

3
Metric System Benefits

• Units are related by powers of 10
• Easy to do conversionsPrefix Multiplier
• Kilo 1000
• Hecta 100
• Deca 10
• deci 1/10
• centi 1/100
• milli 1/1000

4
Conversion Procedure

• Convert 5238 m to Kilometers
• Write the unit equality
• Set up the conversion factor
• The unit you are going to goes on top
• Multiply by conversion factor and cancel units in
  numerator and denominator

5
Multiple Units

• Convert each unit!
• Example Area
• Convert 0.0745 m2 to cm2

6
Multiple Units

• Convert each unit!
• Example Speed
• Convert 83 mi/hr to ft/s

7
Math vs. Science

• Mathematics deals with numbers
• Dont usually deal with measured values
• Numbers are considered infinitely precise or
  exact
• Numbers are obtained by counting or definition
• Science deals with measurements
• Significant figures ARE important
• Is any measure exact?
• Why?

8
Significant Figures

• Indicate precision of a measured value
• 1100 vs. 1100.0
• Which is more precisehow can you tell?
• How precise is each number?
• Precision required dictates the tool required
• More precision ? higher cost

9
The Atlantic and Pacific Rule

• "If a decimal point is Present, ignore zeros on
  the Pacific (left) side. If the decimal point is
  Absent, ignore zeros on the Atlantic (right)
  side. Everything else is significant.
• How many Sig Figs?
• 1.2043
• 0.000569
• 12900

10
Counting Sig FigsThe Gory Detail

• ALWAYS SIGNIFICANT
• Digits from 1-9
• Zeros between two other sig figs
• One or more trailing zeros IF they follow a
  significant figure AND there is a decimal point.
• NOT SIGNIFICANT
• Zeros used as space holders
• Leading zeros or trailing zeros with no decimal
  point
• GIVE THREE EXAMPLES OF EACH RULE!

11
Using Sig Figs

• ADDITION AND SUBTRACTION
• Round the result to the same number of fraction
  digits as in the poorest measurement.
• 74.3123 g
• 73.884? g 72.64??
  g
• 220.84??g

Line up the decimal points!
12
Using Sig Figs

• MULTIPLICATION AND DIVISION
• Round the result to the same number of sig figs
  as in the poorest measurement.
• sig figs
• 8.3124 cm 5
• x 3.10?? cm 3 poorest
• x 4.102? cm 4
• 106. cm3 3

13
Sig Fig Practice

• Take the sig fig quiz at http//antoine.frostburg.
  edu/chem/senese/101/measurement/sigfig-quiz.shtml
• Keep trying until you get 100!