SI - System International

The Metric System

How high is the ceiling?

How high is the ceiling?

1.00.1

Is the ceiling 5 glops high?

A. YesB. No

What must be true of any STANDARD?

•Universally Understood•Repeatable

Old Standards

• Digit• Cubit• Foot• Hands• Stone

What is the problem with these Standards?

Metric System

• Began in 1795 - French• Standardized - 1960

– What does this mean?

• Terms to Know– Fundamental / Derived– Quantity / Unit

Fundamental vs Derived

• Fundamental Units– Base Unit which is defined to be Universally Understood and Repeatable

– 7 Fundamental Units

• Derived– A combination of more than 1 fundamental units

– Examples: m/s; s2; kgm / s2

– Often given an equivalent expression: Newton, Watt, Joule

Quantities vs Units

QuantitiesAmount or how much of a specific dimension

Examples: Length, Mass, Volume, Density

UnitsDescribes the size in which a quantity is measured

Examples: meter, foot, inch, mile

second, hour, minute, millenium

7 Fundamental Units / Quantities

• Length - meter• Mass - kilogram• Time - second• Electric Current - Ampere• Luminous Intensity - candela• Temperature - Kelvin• Amount of Substance - mole

Standard Definition - meterOld Definition

1 m is defined as 10-7 of the distance from the North Pole to the Equator along a line through Lyon, France

New Definition (1960)

1 m is defined as 1650763.63 times the wavelength of orange-red light from a Krypton-86 lamp

Newest Definition (1982)

1 m is defined as the distance light travels in a vacuum in 1/2999792458 of a second

Standard Definition - second

Old Definition

1 s is defined as 1/86400 of a mean solar day

New Definition (1960)

1 s is defined as duration of 9192631770 cycles of the radiation from Cesium-133

Standard Definition - kilogram

Old Definition

1 kg is defined as the mass of water at its densest (T= 4°C) which fills a volume of 1.0 liter

New Definition (1960)

1 kg is defined as mass of a cylinder of platinum-iridium alloy kept at the International Bureau of Weights and Measures near Paris

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Systems of Measurement

• mks - Meter, Kilogram, Second• cgs - Centimeter, Gram, Second• fps - Foot, Pound, Second

Note: These units are fundamental in that system.

What does it mean to be fundamental???

Systems of Measurement

System Length Mass Time ForceWorkEnergy

mksmeter

mkilogram

kgsecond

s

cgsfps

Red = Fundamental

Systems of Measurement

System Length Mass Time ForceWorkEnergy

mksmeter

mkilogram

kgsecond

s

kg m / s^2Newton

N

kg m^2/s^2N*mJoule

Jcgsfps

Red = Fundamental

Systems of Measurement

System Length Mass Time ForceWorkEnergy

mksmeter

mkilogram

kgsecond

s

kg m / s^2Newton

N

kg m^2/s^2N*mJoule

J

cgscentimeter

cmgram

gsecond

sg cm / s^2

dynedyne*cm

erg

fps

Red = Fundamental

Systems of Measurement

System Length Mass Time ForceWorkEnergy

mksmeter

mkilogram

kgsecond

s

kg m / s^2Newton

N

kg m^2/s^2N*mJoule

J

cgscentimeter

cmgram

gsecond

sg cm / s^2

dynedyne*cm

erg

fpsfootft

slugsecond

s

poundlbp

foot poundft lb

Red = Fundamental

Prefixes

Large kilo k 103

Mega M 106

Giga G 109

Tera T 1012 Peta P 1015

Smaller centi c

10-2

milli m10-3

micro µ 10-6

nano n 10-9

pico p 10-12 femto f 10-15

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