The Metric System

Simple & Consistent

Chapter 2, pages 25 - 30

Measurement up to 1790:Not a pretty picture!

•Measurement requires a standardstandard and until about the 1790’s every region had it’s own standards.

Standards• “A standard is something that is

used as a comparison for measuring.

– The standard must be available for available for everyoneeveryone to use when checking measurements. This means a standard a standard should be something in nature that is should be something in nature that is the same all over the earththe same all over the earth.

– The standard must never varynever vary.“

Source =http://www.howe.k12.ok.us/~jimaskew/ps/pmetric.htm

JOHN QUINCY ADAMS - Report to the Congress, 1821

“Weights and measures may be ranked among the necessaries of life to every individual of human society. They enter into the economical arrangements and daily concerns of every family. They are necessary to every occupation of human industry; to the distribution and security of every species of property; to every transaction of trade and commerce; to the labors of the husbandman; to the ingenuity of the artificer; to the studies of the philosopher; to the researches of the antiquarian; to the navigation of the mariner, and the marches of the soldier; to all the exchanges of peace, and all the operations of war.”

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.

Ease of Use - Names

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

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.

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

•10 meters = dekameter•100 meters = hectometer•1000 meters = kilometer

What is a Liter?• The Liter is defined as a

cube measuring 10 centimeters on each side, or 1000 cm3.

• So, the Liter is based on the meter, which is based on the Earth.

10 cm

10 c

m

10 cm

What is a kilogram?

10 cm

10 c

m

10 cm

The mass of 1 Liter of water at 4°C.

Why water?

So, the kilogram is based on the Liter, which is really based on the meter, which is really based on the Earth.

Prototype kilogram in France.

Tiger

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)

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.

Fundamental or Base Units

• Based on an object or event in nature.

• The SI system has 77 fundamental units.

• You already know 4. What are they?

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

Quantity Name Abbreviation

Length meter m

Mass kilogram kg

Temperature kelvin K

Time second s

Luminous Luminous IntensityIntensity

candelacandela cdcd

Electric Electric CurrentCurrent

ampereampere AA

Amount of Amount of SubstanceSubstance

MoleMole molmol

7 Fundamental Quantities of SI7 Fundamental Quantities of SI

What is a second?

The second was originally defined as 1/86,400th of the 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 zero.0 K = Absolute zero.

BP of HBP of H22O = 100O = 100C = 373 C = 373 KKFP of HFP of H22O = 0O = 0C = 273 KC = 273 K

What is a mole?

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

Prefix Symbol

Value Factor Use

Giga G 1,000,000,000

109 Gigabyte

Mega M 1,000,000 106 Megamillion

KiloKilo kk 1,0001,000 101033 kilometerkilometer

deci d 0.1 10-1 decimeter

centicenti cc 0.010.01 1010-2-2 centimetecentimeterr

millimilli mm 0.0010.001 1010-3-3 millimetermillimeter

micro 0.000001 10-6 micrometer

nano n 0.000000001

10-9 nanometer

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