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Measurements and Conversions. Why Measure?. Measurements give specific information Different types: - Base Units: System International Units (or Metric) Standard for many scientific measurements - Derived Units Combinations of base units Ex: density or volume. Metric Units

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why measure
Why Measure?
  • Measurements give specific information
  • Different types:

- Base Units: System International Units (or Metric)

      • Standard for many scientific measurements

- Derived Units

      • Combinations of base units
      • Ex: density or volume
slide3
Metric Units

Mass – the amount of matter in an object, grams (g)

Volume – the amount of space an object occupies, liter (L)

Length – distance between two points, meter (m)

slide5
Converting with metric units
  • K H D __ d c m
  • Place 1 under starting prefix
  • Place 2 under ending prefix
  • Draw an arrow from 1 to 2. This is the direction to move the decimal point.
  • Count the number of places to go from 1 to 2. Be sure to count the __ space.
  • Move decimal point and rewrite number.
slide6
Make the following metric conversions

13.5 g  ___ kg 2.75 mL  ___ L

150 mm  ___cm0.0150 m  ___cm

0.195 cg  ___ mg 0.750 L  ___mL

2.46 mg ___ kg 5.79 HL  ___ L

7.53 km  ___cm0.0432 g  ___mg

4150 cL ___ L 739 dm  ___ m

81.8 cg  ___kg418.2 m  ___ km

slide7
Scientific Notation – a way of showing very large or small numbers.
  • 4.7 x 103 4.7 E 3 4.7 exp3
  • 4.7 x 10 x 10 x 10 = 4,700
  • Only significant numbers remain
  • The “number out front” is only allowed to have one nonzero digit to the left of the decimal point.
converting to scientific notation
Converting TO Scientific Notation
  • Place the decimal after the first digit
  • Count from the original decimal place to the new location.
    • That number will become the exponent.
  • If you counted:
    • To the left (starting # > 1) then + exponent
    • To the right (starting #< 1) then - exponent
  • Write “new” number x 10exponent
  • Do not write any placeholding zeros
    • Non-significant numbers
converting from scientific notation
Converting FROM Scientific Notation
  • The exponent or power tells how many places the decimal point will be moved.
  • If the exponent is positive, the decimal point moves to the right.

- The number will be > 1

  • If the exponent is negative, the decimal point moves to the left.

- The number will be < 1

warm up
Warm-Up
  • Convert the following:

1. 41,300 L to kL

2. 13,200 kg to g

3. 72 cm to mm

    • 41.3 kL
    • 13,200,000g
    • 720mm
warm up1
Warm-Up
  • Express is Scientific Notation:
    • 1600
    • 0.0053
    • 134.8

1. 1.6 x 103

2. 5.3 x 10-3

3. 1.348 x 102

reliability of measurements
Reliability of Measurements
  • Exact numbers - counting numbers

- Not measurements

- A stated value that is certain

      • Example: 100 years = 1 century, 1 foot = 12 inches
  • Measured numbers- have uncertainty because of the equipment/device used and the observer
accuracy and precision
Accuracy and Precision
  • Accuracy

- How close the measured value is to the accepted value

  • Precision

- How close a series of measurements are to each other

significant figures
Significant Figures
  • Scientists use significant figures to show how precisely an experiment was performed
  • Significant Figures (sig figs) – all known digits in a measurement plus one estimated digit.
  • Scientists use rules to determine the number of significant figures in a particular value
when to use sig fig
When to use Sig Fig
  • When something is MEASURED
  • Not when something is COUNTED
coast to coast sig figs
Coast to Coast Sig Figs

Atlantic/Pacific Rule:

  • If a decimal point is absent, count from the Atlantic (right) side starting with the first nonzero digit.
  • If a decimal point is present, count from the Pacific (left) side starting with the first nonzero digit
coast to coast practice
Coast to Coast practice
  • 47.08020
  • 10
  • 5400600
  • 1.158
  • 0.007013
  • 100.
rounding numbers in calculations
Rounding numbers in calculations
  • Add/subtract: the answer will have the same number of places past the decimal point as the measurement with the fewest places past the decimal point.
  • Multiply/divide: the answer will have the same number of sig figs as the measurement with the fewest number of sig figs.
  • Rounding off numbers: 0-4 drop, 5-9 add 1
  • Defined or exact numbers have an infinite number of significant figures.
when to round off significant figures
WHEN to round off significant figures
  • When the rules for rounding change
    • i.e. going from addition  division or

multiplication  addition

  • At the end of the problem, and you are giving the final answer
conversions that you are responsible for knowing
Conversions that you are responsible for knowing…
  • 12 in = 1 ft
  • 3 ft = 1 yd
  • 5280 ft = 1 mile
  • 60 sec = 1 min
  • 60 min = 1 hr
  • 24 hr = 1 day
  • 7 day = 1 wk
  • 365.25 days = 1 yr
  • 16 oz = 1 lb
  • 2000 lb = 1 ton
  • 8 oz = 1 cup
  • 2 cups = 1 pint
  • 2 pints = 1 quart
  • 4 quarts = 1 gallon
unit analysis dimensional analysis
Unit Analysis/Dimensional Analysis
  • A method of converting from 1 set of units to another set of units using a series of conversion factors.
  • A conversion factor is a fraction made from the two parts of the equivalency.
  • 12 in. = 1 ft
  • Each equivalency can produce two conversion factors.
convert 22 inches to feet
Convert 22 inches to feet
  • List possible conversion factors:
  • Set up grid with starting number and units in the upper left side
  • Plug in conversions so that the same units are on the diagonal
unit analysis practice
Unit Analysis Practice
  • 5.75 min  months
  • 135 km  cm
  • 17.5 oz  gal
  • 1.5 mile  inch
  • 145 mg  hg
  • 135 mL  L
slide24
5.75 min  month
  • 5.75 min_ 1 hr 1 day 1 yr 12 mos= 1.31 x 104 months
  • 60 min 24 hr 365.25 day 1 yr
  • 135 km  cm
  • 135 km 1000 m 1 cm = 13,500,000 cm
  • 1 km 0.01 m
  • 17.5 oz  gal
  • 17.5 oz 1 qt 1 gal = 0.138 gal
  • 32 oz4 qt
  • 1.5 mile  inch
  • 1.5 mile 5280 ft 12 in = 95,000 in
  • 1 mile 1 ft
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