The Metric System

Simple & Consistent

Measurement up to 1790:Not a pretty picture!

•Measurement requires a standardstandard

and until about the 1790’s every

region had it’s own standard

Standards• “A standard is something that is

used as a comparison for measuring”

– The standard must be available for available for everyoneeveryone to use to check measurements

– means a standard should be a standard should be something in nature that is the same something in nature that is the same all over the earthall over the earth

– The standard must never varynever vary

1585 – Simon Stevin• Introduced the use of decimals in

mathematics in Europe

•Predicted the universal introduction of decimal coinage, measures and weights

1670 – Gabriel Mouton

•1st to propose the decimal system of measurement based based on the size of the earthon the size of the earth

•Earth-based standard: 1 of longitude

The earth is a standard available to The earth is a standard available to everyone! What an idea!everyone! What an idea!

Systeme International (SI)

•Based on the 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 in 1960

1790 – French Academy of Sciences createdcreated the metric

system

3 Requirements

Basic Standard = Earth

1. The unit of length was to be a portion of the Earth's circumference

Internal Consistency

2. Units for capacity (volume or space) and mass relatedrelated to the unit of length

Ease of Use - Calculations

3. Larger and smaller units are created by multiplying or multiplying or dividing the basic units by dividing the basic units by factors of 10factors of 10

Fundamental or Base Units

•Based on object or event in nature

•The SI system has 77 fundamental units

•You already know 4. What are they?

AbbreviationNameQuantity

mmeterLength

kgkilogramMass

KkelvinTemperature

ssecondTime

cdcdcandelacandelaLuminous Luminous IntensityIntensity

AAampereampereElectric CurrentElectric Current

molmolMoleMoleAmount of Amount of SubstanceSubstance

7 Fundamental Quantities of SI7 Fundamental Quantities of SI

Derived Units

• Combinations of fundamental units• Many, many derived units

• Examples:– Speed or meters/second– Area or Length X Width– Volume or Length X Width X Height– Density or Mass / Volume

Ease of Use - Names

Larger & smaller multiples of each unit named by a series of prefixesprefixes relating them to the base unit

Smaller & Larger Units•1/10 of a meter = decimeter (dm)•1/100 of a meter = centimeter (cm)•1/1000 of a meter = millimeter

(mm)

•10 meters = dekameter (dam)•100 meters = hectometer (hm)•1000 meters = kilometer (km)

UsePowerValueSymbolPrefix

Gigabyte1091,000,000,000GGiga

Megamillion1061,000,000MMega

kilometerkilometer1010331,0001,000kkKiloKilo

decimeter10-10.1ddeci

centimetercentimeter1010-2-20.010.01cccenticenti

millimetermillimeter1010-3-30.0010.001mmmillimilli

micrometer10-60.000001micro

nanometer10-90.000000001nnano

Prefixes in the SI SystemPrefixes in the SI System

Prefixes

•The prefixes can be used with all 7 fundamental units!–Kilometermeter–Milliliterliter–Centigramgram–Microsecondsecond–Nanokelvinkelvin

1790 - Jefferson

•Proposed a decimal-based measurement system for the United States

•Didn’t come up with the prefix idea and his system had too many names

1792 – U.S. Mint

•Produced world’s first decimal currency (one dollar = 100 cents)

What is a meter?

1790: 1/10,000,000 th of the distance from the North pole to the equator

1983: the distance light travels in a vacuum in 1//299,792,458 th of a second

What is a Liter?• Liter defined as cube measuring

10 centimeters on each side, or 1000 cm3

• Liter based on meter, which is based on Earth

10 cm

10 c

m

10 cm

What is a kilogram?

10 cm

10 c

m

10 cm

mass 1 Liter water at 4°C

Why water?

kilogram is based on liter, which is based on meter, which is based on Earth

What is a second?

second was originally defined as 1/86,400th of average solar day

Now: defined in terms of electron transitions in Cs-133

What is a kelvin?

The kelvin is defined in terms of water & absolute zero

0 K = Absolute zero0 K = Absolute zero

bp of Hbp of H22O = 100O = 100C = 373 KC = 373 K

mp of Hmp of H22O = 0O = 0C = 273 KC = 273 K

What is a mole?

•amount of substance which has as many elementary particles as there are atoms in 0.012 kilogram of carbon-12

Prototype kilogram in France