The Metric System

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The Metric System

• Simple Consistent

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Measurement up to 1790Not a pretty picture!

• Measurement requires standard
• and until 1790s
• every region had own standard

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Standards

• standard something used as comparison
• for measuring
• standard must
• be available for everyone to check measurements
• be something in nature that is same everywhere
• never vary

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1585 Simon Stevin

• Introduced use of decimals in Europe
• Predicted universal introduction of decimal
  coinage, measures and weights

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1670 Gabriel Mouton

• 1st to propose decimal system of measurement
  based on size of earth
• Earth-based standard 1? of longitude

Earth is standard available to everyone! What an
idea!
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Systeme International (SI)

• based on metric system
• invented in 1790
• Originally, earth-based standards
• Volume mass linked to length
• Larger smaller multiples of each unit related
  by powers of 10
• updated every few years (particularly 1960 and
  1991)

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1790 French Academy of Sciences created the
metric system

• 3 Requirements

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1Basic Standard Earth

• unit of length is portion of Earth's
  circumference

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2Internal Consistency

• Units for capacity (volume or space) and mass
  related to unit of length

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3Ease of Use - Calculations

• Larger and smaller units created by multiplying
  or dividing basic units by factors of 10

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Fundamental (Base) Units

• Based on object/event in nature
• SI system has 7 fundamental units
• Probably already know 4 of them
• Any guesses as to which ones you know?

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7 Fundamental Quantities of SI
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Derived Units

• Combinations of fundamental units
• Examples
• Speed (meters/second)
• Area (Length x Width)
• Volume (Length x Width x Height)
• Density (Mass / Volume)

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Ease of Use - Names

• Larger smaller multiples of same unit named by
  series of prefixes relating to base unit

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Smaller Units

• 1/10 of meter decimeter (dm)
• 1/100 of meter centimeter (cm)
• 1/1000 of meter millimeter (mm)
• Larger Units
• 10 meters dekameter (dam)
• 100 meters hectometer (hm)
• 1000 meters kilometer (km)

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Prefixes in the SI System
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Prefixes

• used for all 7 fundamental units!
• Kilometer
• Milliliter
• Centigram
• Microsecond
• Nanokelvin

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1790 - Jefferson

• Proposed decimal-based measurement system for
  United States
• Didnt use prefix idea system had too many names

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1792 U.S. Mint

• Produced worlds first decimal currency (one
  dollar 100 cents)

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What is a meter?
1790 1/10,000,000 th of distance from North
pole to equator
1983 distance light travels in vacuum in
1/299,792,458 th of second
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10 cm
10 cm
10 cm
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defined as mass of 1 Liter water at 4C Why
water?
kilogram is based on liter, which is based on
meter, which is based on Earth
10 cm
10 cm
10 cm
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What is a second?
originally defined as 1/86,400th of average solar
day
Now defined in terms of electron transitions in
Cs-133
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What is a Kelvin?
Kelvin is defined in terms of water absolute
zero
0 K Absolute zero bp of H2O 100?C 373 K mp
of H2O 0?C 273 K
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What is a mole?

• amount any substance that has as many elementary
  particles as number of atoms found in 0.012
  kilogram of carbon-12

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Prototype kilogram stored in vault in France