Units of Measurement

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Units of Measurement
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SI Units

• Many of the units you are familiar with, such as
  inches, feet, degrees Farenheit, and cups are not
  units that are used in science
• There was a need to report data that could be
  used and reproduced easily by others
• Metric system was developed in 1795
• Systeme Internationale dUnites
• By using one system of units, scientists can
  quickly interpret the results of one another

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Base Units

• A defined unit in a system of measurements that
  is based on an object or event in the physical
  world

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Quantity Unit Symbol
Length meter m
Mass kilogram kg
Temperature kelvin K
Time second s
Amount of Substance mole mol
Electric Current ampere A
Luminous Intensity candela cd
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Derived Units

• Are a combination of base units
• Example
• The unit for Volume is cubic meters (m3) is a
  derived unit
• You can calculate volume by multiplying length x
  width x height or m x m x m which equals m3

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Quantity Unit Symbol
Area square meter m2
Volume cubic meter m3
Liquid volume cubic decimeter dm3 L
Density kilograms per cubic meter kg/m3
Pressure pascal (kg/ms2) Pa
Energy Joule (kgm2/s2) J
Frequency hertz (1/s) Hz
Electric Charge coulomb (As) C
Speed meters per second m/s
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Metric Prefixes

• Indicates how many times a unit should be
  multiplied or divided by ten

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Large
Small
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Conversion Factors

• Is a ratio of equivalent measurements that is
  used to convert a quantity expressed in one unit
  to another unit
• Will be used to complete your dimensional
  analysis hw worksheet

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Dimensional Analysis

• Also called factor-label method or the unit
  factor method
• A problem-solving method that uses the fact that
  any number or expression can be multiplied by one
  without changing its value.
• The unit factors are conversion factors
• Example any two terms that describe the same or
  equivalent amounts of what we are interested in
• Ex 1 inch 2.54 centimeters
• 1 meter 100 centimeters
• 1 km 1,000 meters

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• 10 megawatts is equal to how many watts?
• 10 MW x 1,000,000 W 10,000,000 W
• 1 1 MW
• 20,000 milligrams is equivalent to how many
  grams?
• 20,000 mg x 1g 20 g
• 1 1,000 mg
• Convert the height of Mount Everest (8,848 m)
  into kilometers
• 8,848 m x 1km 8.848 km or 8.8 km
• 1 1,000 m

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Precision Accuracy

• Precision is a gauge of how exact a measurement
  is
• The more significant figures (reported digits)
  there are, the more precise the measurement
• 5.2 meters vs 5.2345867 meters
• Accuracy is the closeness of a measurement to the
  actual value of what is being measured
• Actual value is 20 cm, are the following
  measurements accurate?
• Measurement 1 19.5 cm
• Measurement 2 10 cm
• Measurement 3 21 cm