Measurement System | CE 007
Measurement System
The most primary thing that an engineer should be well conversant with is the types of measurement systems and
units as well as their conversions. Many quantities are used for the service of
human civilization. Of which, only three quantities of measurements are called primary quantities and others are called secondary quantities. They are as follows:
Primary Quantities :
1. Length 2. Weight 3. Time
Secondary Quantities :
1. Area 2. Volume 3. Angle
4. Work 5. Power 6. Energy
7. Force 8. Heat 9. Light
10. Electricity 11. Illumination etc.
It is interesting to note that quantity angle has not been included in the group of primary quantity.
Primary Quantities :
1. Length 2. Weight 3. Time
Secondary Quantities :
1. Area 2. Volume 3. Angle
4. Work 5. Power 6. Energy
7. Force 8. Heat 9. Light
10. Electricity 11. Illumination etc.
It is interesting to note that quantity angle has not been included in the group of primary quantity.
All these quantities are measured in different
system of units. From ancient times, people of various civilizations in
different parts of the globe had adopted different measuring units at par with
their ease and culture. But at present, only four systems of measurements are
mainly used in scientific, engineering and technological field as given below:
Systems of Measurements :
1. CGS system 2. FPS system
3. MKS system 4. SI system
In CGS system, units of primary quantities i.e., length, weight and time are centimeter, gram and second respectively. The same in FPS system are foot, pound and second respectively. The same in MKS system are metre, kilogram and second respectively. And the same in SI system are metre, Newton and second respectively.
Systems of Measurements :
1. CGS system 2. FPS system
3. MKS system 4. SI system
In CGS system, units of primary quantities i.e., length, weight and time are centimeter, gram and second respectively. The same in FPS system are foot, pound and second respectively. The same in MKS system are metre, kilogram and second respectively. And the same in SI system are metre, Newton and second respectively.
The FPS system of units was primarily originated in Great
Britain and is thus called British system. It is a fraction based system.With a little difference in
magnitudes, it is still in use in U.K, U.S.A and other areas of British
influence.
The CGS, MKS and SI systems are based on metre and hence called Metric system. These systems of units were primarily evolved in France after Renaissance movement and are now used in most part of the world. The advantages of these systems are that these use decimal system of conversions
Since units of all other quantities depend on the units of primary quantities i.e., length, weight and time, it is essential to standardize the definition of these primary quantities.
The CGS, MKS and SI systems are based on metre and hence called Metric system. These systems of units were primarily evolved in France after Renaissance movement and are now used in most part of the world. The advantages of these systems are that these use decimal system of conversions
Since units of all other quantities depend on the units of primary quantities i.e., length, weight and time, it is essential to standardize the definition of these primary quantities.
Definition of Metre
The definition of meter has been modified four times since its inception.
In ancient time, the Greeks used a term called 'metron catholicon' to mean 'a universal measure'. In 17th century, England was accustomed with foot, inch etc. for measurement of length. It was a fraction based system. Going at par with the Greek concept of universal measure, John Wilkins, an English philosopher first proposed a universal length, designating that as 'metre'. At that time, Christian Huygens, a physicist, measured the length of a pendulum with a half period of one second as 39 ¼ inch i.e. 997 mm of the present time. In 1668, John Wilkins proposed to accept that length as a metre.
Another proposal suggested that the distance between the Equator and the North Pole of the earth along a meridian may be accepted as 10,000 kilometer so that one ten-millionth of the length of the earth’s meridian along a quadrant i.e., one ten-millionth of the distance from the Equator to the North Pole can be defined as a metre. In 1791, the French Science Academy selected the meridional definition over the pendulum definition considering that the gravity force varies a little over the surface of the Earth and affects the period of a pendulum.
In ancient time, the Greeks used a term called 'metron catholicon' to mean 'a universal measure'. In 17th century, England was accustomed with foot, inch etc. for measurement of length. It was a fraction based system. Going at par with the Greek concept of universal measure, John Wilkins, an English philosopher first proposed a universal length, designating that as 'metre'. At that time, Christian Huygens, a physicist, measured the length of a pendulum with a half period of one second as 39 ¼ inch i.e. 997 mm of the present time. In 1668, John Wilkins proposed to accept that length as a metre.
Another proposal suggested that the distance between the Equator and the North Pole of the earth along a meridian may be accepted as 10,000 kilometer so that one ten-millionth of the length of the earth’s meridian along a quadrant i.e., one ten-millionth of the distance from the Equator to the North Pole can be defined as a metre. In 1791, the French Science Academy selected the meridional definition over the pendulum definition considering that the gravity force varies a little over the surface of the Earth and affects the period of a pendulum.
In 1889, International Bureau of Weights and
Measures created and presented a new prototype bar made up of an alloy of 90%
platinum and 10% iridium, kept at a temperature of the melting point of ice, distance
between two specific lines of which was defined as a metre. The
original international prototype of the metre is still kept at the office of BIPM
(Bureau Internationale des Poids et Mesures) at Sevres, France under the
conditions specified in 1889.
The International Prototype Metre remained standard
until 1960, when the 11th General Conference of Weights and Measures defined the metre in the new SI system as equal to 1,650,763.73 wave lengths of the orange red emission line in the electromagnetic spectrum of the krypton 86 atom in a vacuum.
This definition was again changed in the 17th General Conference held in 1983. Since by that time it was possible to precisely measure the speed of light in a vacuum as 299,792,458 meters per second, the latest definition of a meter, adopted in 1983, is the distance traveled by light in vacuum in [1/299,792,458] second. This definition of a metre is valid till date.
The definitions of metre are summarized below:
This definition was again changed in the 17th General Conference held in 1983. Since by that time it was possible to precisely measure the speed of light in a vacuum as 299,792,458 meters per second, the latest definition of a meter, adopted in 1983, is the distance traveled by light in vacuum in [1/299,792,458] second. This definition of a metre is valid till date.
The definitions of metre are summarized below:
1st definition : 1668 : A metre is defined as the length of a pendulum with a half period of one second and is equal to 39 ¼ English inch i.e. 997 mm of the present time.
2nd definition : 1791 : A metre is the length equal to one ten-millionth of the distance from the Equator to the North Pole measured along a meridian.
3rd definition : 1889 : A metre is the distance between two specific points of a prototype bar made up of an alloy of 90% platinum and 10% iridium and kept at a temperature of the melting point of ice.
4th definition : 1960 : A metre is equal to 1,650,763.73 wave lengths of the orange red emission line in the electromagnetic spectrum of the krypton 86 atom in a vacuum.
5th definition : 1983 : A metre is equal to a distance traveled by light in vacuum in [1/299,792,458] second.
The spelling of the word metre was originally 'metre' in England but became 'meter' in USA - matching with pronunciation of the Americans. At present majority of the people use it as 'meter'. Spelling metre has been used so far in this post to pay respect to the origin but meter will be used henceforth to keep pace with reality.
2nd definition : 1791 : A metre is the length equal to one ten-millionth of the distance from the Equator to the North Pole measured along a meridian.
3rd definition : 1889 : A metre is the distance between two specific points of a prototype bar made up of an alloy of 90% platinum and 10% iridium and kept at a temperature of the melting point of ice.
4th definition : 1960 : A metre is equal to 1,650,763.73 wave lengths of the orange red emission line in the electromagnetic spectrum of the krypton 86 atom in a vacuum.
5th definition : 1983 : A metre is equal to a distance traveled by light in vacuum in [1/299,792,458] second.
The spelling of the word metre was originally 'metre' in England but became 'meter' in USA - matching with pronunciation of the Americans. At present majority of the people use it as 'meter'. Spelling metre has been used so far in this post to pay respect to the origin but meter will be used henceforth to keep pace with reality.
Definition of Kilogram
A kilogram is defined as a specific weight equal to International Prototype Kilogram (IPK) which is a right circular cylinder of 39.17 mm dia and the same height made up of an alloy of platinum (90%) and iridium (10%). This weight is, in turn, exactly equal to the mass of 1 liter of standard water kept at a temperature of 3.984 degree centigrade under a standard atmospheric pressure.
Definition of Newton
A Newton is defined as the force that would give a mass of 1 kilogram an acceleration of 1 meter per second per second. A Newton is equal to 100,000 dynes.
Definition of Second
A kilogram is defined as a specific weight equal to International Prototype Kilogram (IPK) which is a right circular cylinder of 39.17 mm dia and the same height made up of an alloy of platinum (90%) and iridium (10%). This weight is, in turn, exactly equal to the mass of 1 liter of standard water kept at a temperature of 3.984 degree centigrade under a standard atmospheric pressure.
Definition of Newton
A Newton is defined as the force that would give a mass of 1 kilogram an acceleration of 1 meter per second per second. A Newton is equal to 100,000 dynes.
Definition of Second
The early definition of second was based on the
apparent motion of the sun around the earth. According to that, 1 mean solar
day was taken equal to 24 hours, 1 hour equal to 60 minutes and 1 minute equal
to 60 seconds. Thus a second was accepted as [1/86,400] part of a mean solar day.
But this definition has been modified after the invention of atomic clock. Since 1967, a second has been redefined as the duration of 9,192,631,770 periods of radiation corresponding to transition between two hyper-fine levels of the ground state of a caesium 133 atom.
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But this definition has been modified after the invention of atomic clock. Since 1967, a second has been redefined as the duration of 9,192,631,770 periods of radiation corresponding to transition between two hyper-fine levels of the ground state of a caesium 133 atom.
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Meter এর definition যে just 35 বছর আগে আলাদা ছিল, ভেবে অবাক লাগছে
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