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Measurements: A Brief History
Jens Yap
H3G Phys SLB
The standardization of weights and measures have been the goals of social and economic advance since the ancient times, but is wasn’t until the 18th century where then we created a unified system of measurement. In the ancient times the system of weights were based on human morphology. Which the names of usually the measurements were referred to parts of the human body, but unfortunately because of the inconsistencies of this method (ex. since not every one is equally of the same length or width) they varied from one town to another, from one occupation to another and on the type of object measured.
This lack of a standardized system was a source of error in commercial and social transactions, almost preventing the international commerce and prevented the development of science as an international endeavor. With the expansion of Industry and trade, there was an increasing need for standardization of weights and measurements between countries. Politicians and scientists resolved this situation by adopting a standard measurement (distance and weight) by comparison with a standard (etalon) taken from Nature.
Source: http://www.bipm.org/en/convention/wmd/2004/history.html
meter (m) – LENGTH. Up until 1983 the meter was defined as 1,650,763.73 wavelengths in a vacuum of the orange-red line of the spectrum of krypton-86. And since then it is determined to be the distance traveled by light in a vacuum in 1/299,792,45 of a second.
second (s) – TIME The second is defined as the duration of 9,192,631,770 cycles of the radiation associated with a specified transition of the cesium-133 atom.
kilogram (kg) – MASS The standard for the kilogram is a cylinder of platinum-iridium alloy kept by the International Bureau of Weights and Measures in Paris. A duplicate at the National Bureau of Standards serves as the mass standard for the United States. The kilogram is the only base unit defined by a physical object.
Kelvin (K) and °Celsius (°C) – TEMPERATURE The Kelvin is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water; that is, the point at which water forms an interface of solid, liquid and vapor. This is defined as 0.01 °C on the Celsius scale and 32.02 °F on the Fahrenheit scale. The temperature zero K (Kelvin) is called “absolute zero”.
ampere (A) – ELECTRIC CURRENT The ampere is defined as that current that, if maintained in each of two long parallel wires separated by one meter in free space, would produce a force between the two wires (due to their magnetic fields) of 2 x 10-7 N (Newton) for each meter of length. (a Newton is the unit of force that when applied to one kilogram mass would experience an acceleration of one meter per second, per second).
candela (cd) – LUMINOUS INTENSITY The candela is defined as the luminous intensity of 1/600,000 of a square meter of a cavity at the temperature of freezing platinum (2,042 K).
mole – (mol) AMOUNT OF SUBSTANCE The mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12.
History of Measurement
In the 18th century, people started having a unified measuring system. Initially, they used the human body parts as measurements. They used hands, feet and many others. However, this system was prone to fraud in trading. Measurements are varied in different places. To solve this crisis, scientists decided to use nature as an universal measuring equipment. On April 7, 1795, the French National Assembly defined the term “metre” in a decree. The “metre” was chosen because it can be easily multiplied to the same ratio for larger or smaller items. This was also introduced during the same assembly as the “decimal metric system”. As we all know, this has been the system that most people of the use today.
Length (meter)
- straight distance measurement between two points
Mass (kilogram)
- the amount of matter found in a certain object
Time (second)
- continuous measurement unit that passes through the past, present and future
Electric current (ampere)
- measurement for the amount of electric charge present
Thermodynamic temperature (kelvin)
- a physical description of a state of matter
Amount of substance (mole)
- measurement of the amount of substance found
Luminous intensity (candela)
- measurement for the strength of the wavelength given off by light
Sources:
A Story of Measurement (Just One)
Long ago, in a time where Science was not yet so developed, there was no true ‘fixed’ system of measurement. People would use their bodies to measure – an arm’s length, a foot, a finger. In some kingdoms, it would be the lengths of the King’s parts that would dictate the rule. But some believed the system was flawed because, for starters, people in the world tend to have different proportions.
So, finally, a group of French (I believe) Mathematicians came along and decided to make a standardized length, related to the distance from the north coast to the bottom coast of Europe. Though today, their computations may not be accurate – nor does the meter they created really have a natural basis – they did something we needed very much at the time: make a standard for length.
Most other standard measurement came the same way. As of today, we have the following:
(taken from http://www.unc.edu/~rowlett/units/sifundam.html)
1. Meter – “The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.”
2. Kilogram – “The kilogram is equal to the mass of the international prototype of the kilogram.”
3. Second – “The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.”
4. Ampere – “The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per metre of length.”
5. Kelvin – “The kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.”
6. Mole – “The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.”
7. Candela – “The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.”
Measurements
One of the 1st tools made by man was measurements. They used their body parts such as hands and fingers as a way to measure objects. They needed measurements in tasks such as making houses and they needed to know the right size or shape for this. As time passed the way of measuring became better. One of the measuring systems developed was the english system of measurements. The english measurements were developed from different cultures such as Egyptian, Roman and Anglo-Saxon. Common units in this system of measurements are the inch and foot. After many more years, the Metric system was formed. It was formed during 1790 when the National Assembly of France needed a standard for measurements and weights. This lead to the making of the Metric system. The metric system was made because it was easier to use than the english system of measurements. The different units in the metric system were interrelated making it easier to convert measurements while the english system’s units weren’t interrelated making it hard to use.
The seven basic SI units are meter, kilogram, seconds, ampere, kelvin, mole, and candela. The kilogram is the unit for mass. Seconds is the basic unit for time. Ampere is the basic unit for electric current. Kelvin is the basic unit for temperature. Mole is the basic unit for substance and candela is the basic unit for luminous intensity.
Source:
https://standards.nasa.gov/history_metric.pdf
http://www.hobbyprojects.com/dictionary_of_units/definitions_of_seven_basic_si_units.html
http://www.calculatoredge.com/math/mathfunlib/funlibans21.htm
James Lee H3G
About Measurements
A History of Measurement
Understanding the origins of measurement as a necessity to a functional human society is not particularly difficult, although investigating its development throughout mankind’s history is different and a more arduous pursuit in comparison. For quite a long time, humans naturally used the parts of the body and commonplace objects in their surroundings as a means of measuring things. As even the early societies needed measuring instruments for simple tasks such as the building of structures, creation of clothes, the weighing of objects and trading fair amounts of materials or food, it is understandable that society needed even rudimentary standards of measurement to operate properly.
The first standards for measuring as reflected in early Egyptian documents and Babylonian records were the length of the hand, the finger, the foot and the forearm; the use of visible celestial bodies to measure time is also highly indicated, including the movement of the sun across the sky and the period of time in which the moon shines brightly. Comparing the proportions of water containers and vessels involved filling such containers with plant seeds that were counted later. When scales were developed, stones were used as the standards to weigh against an object.
Due to the relatively shaky nature of these measurement standards however, it is clear that errors and inconsistencies persisted throughout the use of these early measuring tools. Throughout years of argument and dispute regarding the dimensions of a structure, the weight of goods and the time it would take for a caravan to travel this distance. As trade among cultures grew common, the necessity of less variable standards of measurement became apparent. However, there was much disagreement in these standards between societies, and it became difficult to find a consistent and unified system of measurement.
It was not until the eighteenth century that the first universal measurement was conceptualized. A French commission was set up to “deduce an invariable standard for all the measures and all the weights.” Understanding that previous measurements were made by standards that varied greatly depending on individuals, location, et cetera, it sought to devise a system that had a more scientific and universal basis. The pursuit of this universal standard led to the formation of the metre (or meter). This measure is defined as being one ten-millionth (1/10,000,000) of the terrestrial meridian––this being described as the distance from the North Pole to the equator, all points on said distance being along the same geographical longitude. From this measurement was the basis for the measurement of the gram, the cubic metre (or cubic meter), the litre (or liter) and others. These measurements made up what is called the metric system
But even then, the concept of the metre and its resulting measurements was not very widely accepted, as many people were still very much accustomed to use the familiar yet inconstant measures they already had. However, France eventually began to accept this system of measurement and endeavored to make it universal for all nations in the world. This inevitably led to a modernized metric system called the or the International System of Units (the SI units), which perfected the definition of the metre as being based on the constant speed of light––rather than assuming constancy in the size of the earth and using such to determine a standard measure.
While the metric system developed, the British was devising a more scientific “yard” measurement. In contrast to the French, who used first the terrestrial meridian of the earth and then the rate at which light travels, they used the pendulum as a basis. They legalized a standard measurement of the yard based on the properties of the pendulum, having already discovered that the length of the pendulum affected the length of time in which the pendulum would complete a swing. This standard came to be known as the English system of measurement.
To this day, these systems of measurement, having been standardized scientifically, are widely used, being driven to consistency by the common demand for a conventional standard, which in turn was brought about by the universal need for measurement as a necessary tool in society.
The International System of Units (SI)
1. The metre or meter (m)
– to measure length and distance
– the length travelled by light in a vacuum in 1/299,792,458 of a second
2. The kilogram (kg)
– to measure mass
– the mass of the platinum-iridium prototype (a metal used as a standard) kept by the Bureau International Poids et Mesures (BIPM)
3. The second (s)
– to measure time or duration
– the duration of 9,192,631,770 periods of radiation of the caesium (or cesium) 133 atom
4. The kelvin (K)
– to measure thermodynamic temperature
– 1/273.16 of the thermodynamic temperature of the triple point of water
5. The ampere (A)
– to measure electric current
– the constant current maintained in two straight parallel conductors placed 1 metre apart in a vacuum that would produce a force of 2(10^-7) newtons per metre
6. The candela (cd)
– to measure luminous intensity / luminosity
– the luminous intensity in a given direction of a source that emits a radiation frequency of 540*10^12 hertz and a radiation intensity of 1/683 watts per steradian in that direction
7. The mole (mol)
– to measure the quantity or amount of a substance
– the amount of substance containing as many elementary units/entities as there are atoms in 0.012 kilograms (12 grams) of carbon 12
References:
https://standards.nasa.gov/history_metric.pdf
http://www.bipm.org/en/convention/wmd/2004/history.html
http://www.cftech.com/BrainBank/OTHERREFERENCE/WEIGHTSandMEASURES/MetricHistory.html
http://www.french-metrology.com/en/history/history-mesurement.asp
http://www.french-metrology.com/en/si/units-measurement.asp
http://www.ebyte.it/library/educards/siunits/TablesOfSiUnitsAndPrefixes.html
Timeline of Measurements
The International System of Units was created in order to make the unit of measurements more precise. The beginning of this internationally accepted system was believed to be during the 18th century when the French Revolution was taking place. They were able to develop the decimal metric system that would be the basis of the whole system of units. Later on, through the efforts of several scientists and mathematicians, notably Gauss, Thompson, Maxwell and Giorgi, they were able to set a standard for the electrical…
Before we had the measuring system we know of now, people used to use their limbs to measure any amount of an object. This way of measuring was very unreliable because everybody had a unique measurement and some could cheat their way by saying that this was their measurement when it was supposed to be more.
This changed during the French Revolution. The International Unit of Systems was invented in 1799 containing two of the S.I. units, the “kilogram” and the “meter”. Soon, the “second” would be added for time, the “ampere” for electrical currents, the “kelvin” for temperature, the “candela” for the intensity of light and lastly the “mole” for the amount of substance. These paved the way for a internationally recognized system of measurements and could facilitate in fairer and more precise measurements of any kind. I believe that there will be more measurements to come for discoveries that are yet to be made. One way or another, our system of measurements will become even more concise and credible for the years to come.
S.I. Units:
Meter:
Sources:
History of Measurements
Before standardized measurements, it was difficult to conduct measurements since it varied from place to place. A lot of the measurements they created used body parts, and as we know, that obviously differs from person to person. It was very inaccurate.
Standardized measurement was made by the Mesopotamia although it was the Greeks that created the scientific basis for measurements. The metric system was introduced by The French during 1790 and used throughout the 1800s.
There are 7 SI Units:
Meter- A meter is the basic unit of length in the SI. It is measured with the symbol (m)
Kilogram- A kilogram is the basic unit of weight in the SI. It is measured with the symbol (kg)
Second- A second is the basic unit of time in the SI. It is measured with the symbol (s)
Kelvin- A kelvin is the basic unit of temperature in the SI. It is measured with the symbol (K)
Mole- A mole is the base unit in measuring amount of substance in the SI. It is measured with the symbol (mol)
Ampere- An ampere is the base unit in measuring electrical current in the SI. It is measured with the symbol (A)
Candela- A candela is the base unit in measuring the intensity of light in the SI. It is measured with the symbol (cd)
Sources:
http://www.sciencemadesimple.com/metric_system.html
http://lamar.colostate.edu/~hillger/unit-definitions.html#ampere
Physics SL B 