Unit names
The metric system was first developed in France during
the French Revolution. A French law passed in 1795
defined five units of measure. Three of these names are
still in use today. They are the metre which is the unit
of length, the gram which is the unit of mass and the
litre which is the unit of volume. Since then many other
units of measure have been developed and many
definitions changed. The metric system now has units of
measurement for energy, power, force, electric current,
radioactivity and many others. The most commonly used
units of measure in the metric system are listed below.
Length
In the metric system, length is measured in metres. The
symbol for the metre is the letter "m". The metre was
originally defined as being 1⁄10,000,000 of the distance
between the North Pole and the Equator on the meridian
that passed through Paris. In 1799, a platinum bar that
was equal to this length was made and became the
"prototype metre"
Volume
In the metric system, volume is measured in litres. The
symbol for the litre is "L". In 1795 the French
Government defined one litre as being the same volume as
the volume of a cube which had sides that were 10
centimetres (3.9 in).
Mass
In the metric system, mass is measured in grams. The
symbol for the gram is the letter "g". In 1795 the
French Government defined the gram as the mass of one
cubic centimetre of water at the freezing point of ice.
This was difficult to measure, so in 1799 the French
Government made a "prototype kilogram" (1,000 grams or
35 ounces) mass.
Temperature
In the metric system, temperature is measured in degrees
Celsius. The symbol for degrees Celsius is "°C". Water
freezes at "0 °C (32 °F)" and boils at "100 °C (212
°F)".
Time
In the metric system, the unit of time is the seconds.
The second was first used as part of the metric system
by Carl Friedrich Gauss in 1832.
The definitions of the units are often being changed. In
1960 the definition of the metre was changed. Since then
it has been defined in terms of the speed of light. In
2019, the kilogram is redefined in terms of the Planck
constant. |
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Prefixes
If the numbers are too big or too small, the metric
system uses prefixes to make it easier to understand the
numbers. |
- milli
- The prefix milli is used to show that a
measurement is 1⁄1000 (or 0.001) of the base
measurement:
- There are 1000 milligrams (mg)
in a gram.
- There are 1000 millimetres (mm)
in a metre.
- There are 1000 millilitres (mL)
in a litre.
- centi
- The prefix centi is used to show that a
measurement is 1⁄100 (or 0.01) of the base
measurement:
- There are 100 centimetres (cm)
in a metre.
- There are 100 centilitres (cL)
in a litre.
- kilo
- The prefix kilo is used to show that a measurement
is 1000 times as large of the base measurement:
- There are 1000 grams in a
kilogram (kg).
- There are 1000 metres in a
kilometre (km).
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There are a lot of other prefixes. Some of them are: |
- micro
which means one millionth (1⁄1,000,000). The symbol
for "micro" is the Greek letter μ (called "mu").
- deci
which means one tenth (1⁄10). The symbol for "deci"
is "d".
- mega
which means one million (1,000,000). The symbol for
"mega" is "M". Care must be taken not to get "m"
(for "milli") and "M" (for "mega") mixed up.
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British and American spelling
Some names in the metric system are spelt differently in
British English and in American English. |
- The word metre is used in British
English while the word meter is used in American
English.
- The word litre is used in British
English while the word liter is used in American
English.
- The word gram is used in both
British English and in American English. The word gramme
can also be used in British English, but many British
people think that this is old-fashioned.
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Administering the metric system
In 1875 representatives from the governments of twenty
different countries met in Paris to discuss weights and
measures. Seventeen of the countries signed a treaty about
weights and measures. The treaty was called "The Convention
of the Metre". The countries that signed were: Argentine
Confederation, Austria-Hungary, Belgium, Brazil, Denmark,
France, Germany, Italy, Peru, Portugal, Russia, Spain,
Sweden and Norway, Switzerland, Turkey, United States and
Venezuela. They agreed: |
- To set up an inter-governmental
organisation to administer the treaty. This organization
was called the International Bureau of Weights and
Measures (BIPM).
- France was to have responsibility
for acquiring suitable premises for the BIPM. These
premises would become neutral territory. The BIPM
offices and laboratories would be located on the site.
- To make 40 identical copies of the
kilogram. One was chosen as the prototype (or primary)
copy. This copy was known as the "International
Prototype Kilogram". It replaced the Kilogramme des
archives as the world's primary copy of the kilogram.
The Kilogramme des archives would be kept at the BIPM
premises.
- To make 30 identical copies of the
metre. One was chosen as the prototype (or primary)
copy. This copy was known as the "International
Prototype Metre". It replaced the Metre des archives as
the world's primary copy of the metre. The Metre des
archives would be kept at the BIPM premises.
- To give one copy of the metre and
one copy of the kilogram to each country. These would be
called "national prototype metres" and "national
prototype kilograms".
- To compare the national prototype
metres and kilograms against the international
prototypes at regular intervals.
- To promote the use of the metric
system.
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The United Kingdom and the Netherlands went to the
conference but did not sign the treaty at that time. After
further consideration, the United Kingdom did sign the
treaty in 1884 and the Netherlands became a member in 1929.
In 1889 the copies of the kilogram and the metre were ready
to be given to the different countries that signed the
treaty.
The United States Congress ratified the treaty in 1878. The
United Kingdom signed the treaty 1884. Neither country
passed laws making it compulsory to use the metric system.
In 1921 the Metre Convention was extended to include all
physical measurements including time, electricity and
temperature.
In 1960 the BIPM published the "International System of
Units" (or SI). SI clarified a number of areas of the metric
system, particularly in science and in engineering. The BIPM
also standardized the way in which SI was written making it
the same for all languages.
History
There are 16 US fluid ounces in a US pint but there are 20
imperial [UK] fluid ounces in an imperial pint. The US fluid
ounce is larger than the imperial fluid ounce, but the
imperial pint is larger than the US pint. In the 1700's this
type situation was common across Europe. Each country
measured length, weight/mass and volume in its own way.
Sometimes different countries or cities used the same name
for different measurements. Sometimes different cities in
the same country had different ways of measuring things. In
1789 there were a quarter of a million different units of
weight and measure in France.
French Revolution
During the French Revolution, French scientists decided that
it would be better to have a new system of weights and
measures. The system would be the same in all French
provinces and cities. They also decided that it would be
easier if the new system used 10's instead of 12's, 16's or
20's, because people normally count in 10's. The new system
became the official system of measurement in France in 1799.
One of the French leaders, the Marquis de Condorcet declared
that "[the metric system] is for all people for all time".
They decided that the new system would be for everybody on
Earth and that the new unit of length would be called a "metre".
They decided there would be 10,000 kilometres (6,200 miles)
between the North Pole and the equator. Between 1791 and
1798 two surveyors, Pierre Méchain and Jean-Baptiste
Delambre, measured the distance between the cities of
Dunkirk to Barcelona using old French units, and used the
stars to measure their latitudes. They used this information
to work out that the length of the metre should be 443.296
lignes. In 1798 the French scientists made a bar of platinum
that was exactly one metre long. They stored this bar in the
French archives. It was called the metre des archives.
People who made one metre rulers were able to check that
their rulers were the same length as the metre des archives.
Other scientists made a kilogram weight from platinum which
was also put in the archives. This weight was called the
kilogram des archives.
First attempt to metricate
France
In 1799 the metric system was made compulsory, meaning
people were made to use it by law, in the region around
Paris. This caused a lot of confusion because the police
enforced the new measures but customers preferred the old
ones. So shopkeepers had to have both. People became worried
the new measures were used to cheat them. Politicians tried
to educate and convince people to use metric, but the people
rejected the metric system. In 1800 the government tried to
make the system acceptable by changing the names of the
units back to the simpler names used before metrication. For
example, the decimetre, centimetre, and millimetre were
renamed to palme (hand), doigt (finger) and trait (trace).
In 1799 Napoleon became the leader of France. By 1812 he had
conquered most of Europe. He introduced the metric system to
the countries that he conquered. In 1815 he was defeated at
the Battle of Waterloo. After Napoleon was defeated, most of
the countries started using their old systems of measurement
again.
During this time, the metric system was still the official
system of measurement in France. And it still had simplified
unit names. But the French people continued to use the
measures they were used to. The French government tried to
persuade the people to convert. They mass-produced metric
rulers. They tried to teach the people to use metric
measures, and commanded the police to punish people who
would not cooperate. Eventually the government stopped
trying and withdrew the metric system.
France abandon the metric system
On 12 February 1812, France stopped using the metric system
and started using a new system called mesures usuelles. The
new system was based on many of the old pre-metric units.
The old units were redefined to be round numbers or
fractions of the withdrawn metric units. For example the
livre (pound) was reintroduced and changed from 489 grams to
500 grams. The toise was redefined as 2 metres. The toise
contained 6 pied (feet), changed from 324.8 mm to 1⁄3 of a
metre (333.33 mm). The pied had 12 pouces (inches) and the
pouce had 12 lignes.
Second attempt to metricate
France
In 1837 the metrication laws were revived in France. And in
1840, the system did become compulsory throughout France,
almost 50 years after it was first introduced.
Wider adoption of the metric system
During the nineteenth century many small countries started
cooperating with each other. In 1815 the Kingdom of the
Netherlands was formed from seventeen small states. Each
state had its own system of measurement. In 1820 they
decided that it would be better if everybody used the metric
system.
In 1815 the German Confederation was formed. It was an
association of 39 different states. Each state had its own
system of measurements. In 1834 the German Confederation
formed a customs union called the Zollverein. In 1851 the
Zollverein decided to use metric units for trade between the
various states. In 1871, most of the states in the German
Confederation were joined together to form the German
Empire. The German Empire continued to use the metric
system.
In the same year, Italy was also formed from a large number
of small states. Italy also decided to use the metric system
rather than choosing one of the old systems of measurement.
By 1875 many European and Latin American counties were
already using the metric system. These countries included
France, Germany, Italy, Spain, Portugal, Brazil, Mexico,
Argentina, Peru and Columbia. Between 1875 and 1914 many
more countries including Norway, Sweden, Denmark, Finland,
Paraguay, Philippines and Vietnam started to use the metric
system. In 1917, during the Bolshevik Revolution, the USSR
(now Russia) adopted the metric system. By the start of the
Second World War most non-English speaking countries had
adopted the metric system.
United States
In 1866, after most of the South American countries started
to use the metric system, the United States passed a law
that allowed people to use either the metric system or
United States customary units for trade. Before 1893 the
yard was defined as the length of the "standard yard" which
was kept by the United States Treasury. The pound was
defined as being the mass of the "standard pound". In 1893
the United States Congress passed the Mendenhall Order. This
order defined the yard as being exactly 3600⁄3937 metres and
the pound as being exactly 0.4535924277 kilogram. The order
only changed the definitions of the pound and the yard. It
had no other effect on people's lives.
In 1975 the Metric Conversion Act started a formal
metrication process. Metrication was to be voluntary. It was
to be coordinated by the U.S. Metric Board. In 1988 the
Omnibus Trade and Competitiveness Act said that metric units
had to be used for all federal projects. The Act did not
apply to state projects. Some states demanded that metric
units be used but other states did not. Some industries
changed to using metric units but others did not. Soft
drinks are sold in metric quantities. Milk is sold in
customary units. Metric units are widely used in the design
of motor cars. Aircraft such as the Boeing 787 Dreamliner
were designed using mainly customary units.
Some people in the United States want to complete the
change-over to the metric system. They say that it will make
things easier for everybody. Other people say that it will
cost too much money. Some people want to use the metric
system because it will make it easier to export goods. Other
people say that metrication can only work if all fifty
states metricate at the same time. This will not happen
unless the Federal Government takes the lead.
United Kingdom
In 1897 the United Kingdom passed a law allowing people to
use either the metric system or Imperial units for trade. By
the late 1960s three quarters of British exports were to
countries that used the metric system. However people in the
United Kingdom still used imperial units. The Metrication
Board was set up in 1969 to help Britain change to the
metric system. Each company had to pay their own expenses.
Some companies saved a lot of money by changing to the
metric system because they could make the same goods for
export as they made for sales in the United Kingdom. For
example, almost all motor cars use metric-sized nuts and
bolts. Other companies lost money because they had to make
many changes but did not have any benefit from the changes.
When the Metrication Board was closed down in 1981 most of
government and industry had changed to the metric system but
a lot of everyday things like road signs had not been
changed. A survey taken in 2013 showed that metric units and
imperial units were both widely used by British people in
their private lives. |
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 Kiddle: Metric System
Wikipedia: Metric System |
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