CGPM produced the SI, which was based on six fundamental quantities,
and their units were adopted in 1954 at the Tenth General Conference of
Weights and Measures: meter (m) for length, kilogram (kg) for mass, second
(s) for time, ampere (A) for electric current, degree Kelvin (°K) for
temperature, and candela (cd) for luminous intensity (amount of light). In
1971, the CGPM added a seventh fundamental quantity and unit: mole
(mol) for the amount of matter.
Based on the notational scheme introduced in 1967, the degree symbol
was officially dropped from the absolute temperature unit, and all unit
names were to be written without capitalization even if they were derived
from proper names (Table 1–1). However, the abbreviation of a unit was to
be capitalized if the unit was derived from a proper name. For example, the
SI unit of force, which is named after Sir Isaac Newton (1647–1723), is
newton (not Newton), and it is abbreviated as N. Also, the full name of a
unit may be pluralized, but its abbreviation cannot. For example, the length
of an object can be 5 m or 5 meters, not 5 ms or 5 meter. Finally, no period
is to be used in unit abbreviations unless they appear at the end of a sentence.
For example, the proper abbreviation of meter is m (not m.).
The recent move toward the metric system in the United States seems to
have started in 1968 when Congress, in response to what was happening in
the rest of the world, passed a Metric Study Act. Congress continued to promote
a voluntary switch to the metric system by passing the Metric Conversion
Act in 1975. A trade bill passed by Congress in 1988 set a September
1992 deadline for all federal agencies to convert to the metric system. However,
the deadlines were relaxed later with no clear plans for the future.
The industries that are heavily involved in international trade (such as the
automotive, soft drink, and liquor industries) have been quick in converting
to the metric system for economic reasons (having a single worldwide
design, fewer sizes, smaller inventories, etc.). Today, nearly all the cars
manufactured in the United States are metric. Most car owners probably do
not realize this until they try an English socket wrench on a metric bolt.
Most industries, however, resisted the change, thus slowing down the conversion
process.
Presently the United States is a dual-system society, and it will stay that
way until the transition to the metric system is completed. This puts an extra
burden on today’s engineering students, since they are expected to retain
their understanding of the English system while learning, thinking, and
working in terms of the SI. Given the position of the engineers in the transition
period, both unit systems are used in this text, with particular emphasis
on SI units.
As pointed out, the SI is based on a decimal relationship between units.
The prefixes used to express the multiples of the various units are listed in
Table 1–2. They are standard for all units, and the student is encouraged to
memorize them because of their widespread use
CGPM produced the SI, which was based on six fundamental quantities,
and their units were adopted in 1954 at the Tenth General Conference of
Weights and Measures: meter (m) for length, kilogram (kg) for mass, second
(s) for time, ampere (A) for electric current, degree Kelvin (°K) for
temperature, and candela (cd) for luminous intensity (amount of light). In
1971, the CGPM added a seventh fundamental quantity and unit: mole
(mol) for the amount of matter.
Based on the notational scheme introduced in 1967, the degree symbol
was officially dropped from the absolute temperature unit, and all unit
names were to be written without capitalization even if they were derived
from proper names (Table 1–1). However, the abbreviation of a unit was to
be capitalized if the unit was derived from a proper name. For example, the
SI unit of force, which is named after Sir Isaac Newton (1647–1723), is
newton (not Newton), and it is abbreviated as N. Also, the full name of a
unit may be pluralized, but its abbreviation cannot. For example, the length
of an object can be 5 m or 5 meters, not 5 ms or 5 meter. Finally, no period
is to be used in unit abbreviations unless they appear at the end of a sentence.
For example, the proper abbreviation of meter is m (not m.).
The recent move toward the metric system in the United States seems to
have started in 1968 when Congress, in response to what was happening in
the rest of the world, passed a Metric Study Act. Congress continued to promote
a voluntary switch to the metric system by passing the Metric Conversion
Act in 1975. A trade bill passed by Congress in 1988 set a September
1992 deadline for all federal agencies to convert to the metric system. However,
the deadlines were relaxed later with no clear plans for the future.
The industries that are heavily involved in international trade (such as the
automotive, soft drink, and liquor industries) have been quick in converting
to the metric system for economic reasons (having a single worldwide
design, fewer sizes, smaller inventories, etc.). Today, nearly all the cars
manufactured in the United States are metric. Most car owners probably do
not realize this until they try an English socket wrench on a metric bolt.
Most industries, however, resisted the change, thus slowing down the conversion
process.
Presently the United States is a dual-system society, and it will stay that
way until the transition to the metric system is completed. This puts an extra
burden on today’s engineering students, since they are expected to retain
their understanding of the English system while learning, thinking, and
working in terms of the SI. Given the position of the engineers in the transition
period, both unit systems are used in this text, with particular emphasis
on SI units.
As pointed out, the SI is based on a decimal relationship between units.
The prefixes used to express the multiples of the various units are listed in
Table 1–2. They are standard for all units, and the student is encouraged to
memorize them because of their widespread use
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