Introduction to the Metric System

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Introduction to the Metric System
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Introduction
The metric system is a group of units used to
make any kind of measurement, such as length,
temperature, time, volume, or weight. No other
system of measurement ever used equals the metric
system in simplicity. Scientists everywhere make
measurements in metric units, and so do all other
people in most countries.
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Introduction
A group of French scientists created the metric
system in the 1790's. Since then, the system has
been revised several times. The official name of
the present version is Systeme International
d'Unites (International System of Units), usually
known simply as SI. The term metric comes from
the base unit of length in the system, the meter,
for which the international spelling is metre.
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The Creation of the Metric System
In 1790, the National Assembly of France asked
the French Academy of Sciences to create a
standard system of weights and measures. A
commission appointed by the academy proposed a
system that was both simple and scientific. This
system became known as the metric system, and
France officially adopted it in 1795. But the
government did not require the French people to
use the new units of measurement until 1840.
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The Creation of the Metric System
In the original metric system, the unit of length
equaled a fraction of the earth's circumference.
This fraction was 1/10,000,000 of the distance
from the North Pole to the equator along a line
of longitude near Dunkerque, France and
Barcelona, Spain. The French scientists named
this unit of length the metre, from the Greek
word metron, meaning a measure.
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The Creation of the Metric System
It is interesting to note that a portion of the
earths surface was actually measured and the
entire distance calculatedassuming the earth was
a perfect sphere. Later, an iridium alloy bar
was cast with two lines etched along the ends.
The distance between these lines was the standard
meter.
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The Creation of the Metric System
The units for capacity and mass came from the
meter. The commission chose the cubic decimeter
as the unit of fluid capacity and named it the
liter. A liter is a cube that is one decimeter
on each side. The scientists defined the unit
for mass, the gram, as the mass of a cubic
centimeter of water at the temperature where it
weighs the most. That temperature is about 4 C
(39 F).
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Using the Metric System
The scientists who created the metric system
designed it to fit their needs. They made the
system logical and exact. Furthermore, it is
necessary to know only a few metric units to make
everyday measurements.
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Using the Metric System
The metric system is simple to use for two
reasons. First, it follows the decimal number
system--that is, metric units increase or
decrease in size by 10's. For example, a meter
has 10 parts called decimeters. A decimeter has
10 parts called centimeters. Units in the
inch-pound system have no single number
relationship between them. For example, feet and
yards are related by 3's, but feet and inches are
related by 12's.
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Using the Metric System
The metric system is a decimal system just as are
the U.S. and Canadian money systems. In a
decimal system, a unit is 10 times larger than
the next smaller unit. For example, a meter
equals 10 decimeters just as a dollar equals 10
dimes.
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Using the Metric System
Also, the metric system has only 4 base units
that make up all its measurements. The
inch-pound system has more than 20 base units for
just its common measurements. Inch-pound units
used for special purposes add many, many more
base units to that system.
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Metric Units of Measure
Four base (basic) units form the foundation of
the metric system. Nearly all everyday
measurements involve only four of these units.
The meter is the base unit for length or
distance.
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Metric Units of Measure
The kilogram is the unit for mass, which is the
weight of an object if its measured on earth.
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Metric Units of Measure
The second is the base unit for time.
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Metric Units of Measure
The Kelvin is the base unit for temperature.
Most people, when measuring in metric units, use
Celsius temperatures instead of Kelvin
temperatures. One Kelvin is equivalent to one
degree Celsius, but the two temperature scales
begin at different points.
NASA has been able to get down to 1 degree above
absolute zero.
Thats -272 degrees Celsius!
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Metric Prefixes
Most metric units have a prefix that tells the
relationship of that unit to the base unit. These
prefixes are the same no matter which base unit
is used. This uniform system also simplifies
metric measurement.
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Metric Prefixes
Greek prefixes are used to show multiples of a
base unit. They make a base unit larger. For
example, deka means 10 times, hecto means 100
times, and kilo means 1,000 times.
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Metric Prefixes
Latin prefixes are used to show the submultiples
of the base unit. They make a base unit smaller.
For example deci means 1/10, centi means 1/100
and, milli means 1/1,000.
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Length and Distance
The meter is used for such measurements as the
length of a rope or of a piano or other large
object. It also is used to measure the height of
a mountain or the altitude of an airplane.
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Length and Distance
Some short lengths are measured in centimeters.
Books, pencils, and other small objects may be
measured in centimeters.
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Length and Distance
Very small things are measured in millimeters.
Photographic film, small hardware, and tiny
mechanical parts are measured in millimeters.
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Length and Distance
Long distances, such as those between cities, are
measured in kilometers. A kilometer is
approximately ten times the length of a football
field - including the end zones.
A short distance, such as that between two
buildings on the same block, is measured in
meters.
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Measuring Area
Surface measurements tell how much area something
covers. For example, the amount of carpeting
needed to cover a floor is measured in square
units. Most areas are measured in square meters.
A square meter equals the surface covered by a
square one meter long on each side. (Some of the
pro basketball players are nearly 2 meters tall!)
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Measuring Area
Large land areas, such as cities and countries,
are measured in square kilometers.
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Measuring Area
Small areas may be measured in square centimeters.
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Measuring Area
Tiny areas may be measured in square millimeters.
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Volume and Capacity
Volume and capacity measurements tell how much
space something occupies or encloses. A volume
measurement tells the size of a box, and a
capacity measurement tells how much the box can
hold. Volume and capacity are both measured in
cubic units, such as cubic meters or cubic
decimeters. The volume of a box with each side 1
meter long equals 1 cubic meter. A cubic meter
contains 1,000 cubic decimeters.
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Volume and Capacity
Most capacity measurements for liquids are made
in units called liters. A liter equals a cubic
decimeter.
Four people could comfortably share a liter of
milk during dinner.
Many countries pump their gas in liters.
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Volume and Capacity
A deciliter (1/10th of a liter) could measure a
serving of juice for a baby.
But hey! Nobody measures stuff in deciliters!
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Volume and Capacity
The milliliter (1/1000th of a liter) is used to
measure smaller amounts of liquid.
A milliliter equals a cubic centimeter.
We use a graduate cylinder to measure milliliters
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Weight and Mass
The mass of an object is not really the same as
its weight because its weight changes with
altitude. However, the two measurements are
equal at sea level on the earth. The kilogram is
a unit of mass. But most people who use the
metric system think of the kilogram as a unit of
weight.
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Weight and Mass
A kilogram is equal in mass to a liter of water.
Kilos are used to measure larger weights.
This elephant weighs 2,837 kilos!
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Weight and Mass
The gram is used for small weight measurements.
A gram equals 1/1,000 of a kilogram.
Grams can be used to measure individual portions
of food.
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Weight and Mass
For extremely small amounts, the milligram is
used.
The dose of an aspirin tablet and other medicines
are measured in milligrams.
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Time
The metric system measures time just as the
inch-pound system does for measurements longer
than a second, For such measurements, the
metric system does not follow the decimal system.

For example, 60 not 100 seconds equal a
minute, and 60 minutes equal an hour. Time
measurements in both systems use a decimal
arrangement for units longer than a year. Ten
years equal a decade, 10 decades are a century,
and 10 centuries are a millennium.
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Time
The metric system follows a decimal arrangement
for time measurements shorter than a second.
Scientists and others who work with electronic
equipment, including computers and radar, use
such measurements.
For example, some electronic computers perform
mathematical operations in microseconds and
nanoseconds. A microsecond is 1/1,000,000 of a
second, and a nanosecond is 1/1,000,000,000 of a
second.
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Temperature
Most people who use the metric system have
thermometers that are marked in degrees Celsius
(C). Water freezes at 0 C and boils at 100 C.
The normal body temperature of human beings is 37
C.
Celsius has been the official name of the metric
scale for temperature since 1948. But many
people still call this scale by its old name of
centigrade scale.
The word centigrade means divided into 100
parts. The Celsius scale has 100 degrees
between the freezing and boiling temperatures of
water.
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Temperature
Scientists do not know of any limit on how high a
temperature may be.
The temperature at the center of the sun is about
15,000,000 C.
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Temperature
However, nothing can have a temperature lower
than 273C. This temperature is called
absolute zero. It forms the basis of the Kelvin
scale used by some scientists.
One degree Celsius equals one Kelvin. Because
the Kelvin scale begins at absolute zero, 0 K
equals 273C, and 273 K equals 0 C.
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Original text taken from The Metric System,
World Book, Millennium 2000 - modified by Tim
Paterek. ? 1999 World Book, Inc.