Metric System Simple &

Consistent

Measurement up to 1790:not a pretty picture!

measurement requires a recognizable standardstandard for all but… until 1790’s every region had own standards

Standards• “standard: something used as

comparison for measuring”

– standard must:•be available for everyoneavailable for everyone to check measurements

•be something in nature that be something in nature that isis same same everywhereeverywhere

•never varynever vary

1585 – Simon Stevin• introduced use of decimals in

Europe– allows for parts of a whole

•predicted universal introduction of decimal coinage, measures and weights

1670 – Gabriel Mouton•1st to propose decimal system of

measurement based on size of based on size of earthearth

•Earth-based standard: 1of longitude Earth is standard Earth is standard

available to everyone! available to everyone! What an idea!What an idea!

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 (major changes in 1960 and 1991)

1790 – French Academy of Sciences createdcreated the metric

system

3 Requirements

# 1Basic Standard = Earth

•unit of length is portion of Earth's circumference

#2Internal Consistency

•units for capacity (volume/space) and mass relatedrelated to unit of length

#3Ease of Use - Calculations

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

Fundamental (Base) Units

•based on object/event in nature

•SI system has 77 fundamental units

•probably already know 4 of them• any guesses as to which ones you know?

ABBREVIATIONUNITQUANTITY

mmeterlength

kgkilogrammass

Kkelvintemperature

ssecondtime

cdcdcandelacandelaluminous intensityluminous intensity

AAampereampereelectric currentelectric current

molmolmolemoleamount of amount of substancesubstance

7 Fundamental Quantities of SI7 Fundamental Quantities of SI

Derived Units

• combinations of fundamental units

• examples:– speedspeed (meters/second)– areaarea (length x width)– volumevolume (length x width x height)– densitydensity (mass / volume)

Ease of Use - Names

larger & smaller multiples of same unit named by

series of prefixesprefixes relating to base unit

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)

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

•used for all 7 fundamental units!–kilometermeter–milliliterliter–centigramgram–microsecondsecond–nanokelvinkelvin

1790 - Jefferson• proposed decimal-based measurement

system for US

cons:

no prefixes

& too many

names

1792 – U.S. Mint

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

• 100 cents in dollar• 4 quarters in dollar• 10 dimes in dollar• 20 nickels in dollar

can see how this can be confusing:-names not related to each other -no consistency with parts of dollar

What is a What is a meter?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

What is a LiterLiter?• defined as cube

measuring 10 centimeters on each

side (1000 cm3)

10 cm

10 c

m

10 cm

•liter based on meter, which is based on Earth

What is a kilogramkilogram?

10 cm

10 c

m

10 cm

defined as mass of 1 liter water at 4°C

Why waterWhy water?

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

What is a secondsecond?originally defined as 1/86,400th of average solar day

defined now in terms of electron transitions in Cs-133

What is a KelvinKelvin?

Kelvin is defined in terms of water & absolute zero

0 K = Absolute zero0 K = Absolute zero

bp of Hbp of H22O = 100C = 373 O = 100C = 373 KKmp of Hmp of H22O = 0C = 273 O = 0C = 273 KK

What is a mole mole?

amount any substance that has as many particles as # atoms found in 0.012 kg of carbon-12

prototype kilogramkilogram stored in vault in France