Massa

kilogrammo, kg

Anubis ThothAmmit

Temperatura

grado centigrado, °C, e grado kelvin, K

Temperatura

grado centigrado, °C, e grado kelvin, K

strumenti analogici

strumento digitale

Unità di misura del S.I. lunghezza ⇒ metro (m)

tempo ⇒ secondo (s)

massa ⇒ kilogrammo (kg)

temperatura ⇒ grado kelvin (K)

348 b units , measurements and constants

monochromatic radiation of frequency 540 ⋅1012 hertz and has a radiant intensity in thatdirection of (1/683) watt per steradian.’ (1979)*

Note that both time and length units are defined as certain properties of a standard ex-ample of motion, namely light. In other words, also the Conférence Générale des Poidset Mesures makes the point that the observation of motion is a prerequisite for the defini-tion and construction of time and space.Motion is the fundament each observation andmeasurements. By the way, the use of light in the definitions had been proposed alreadyin 1827 by Jacques Babinet.*

From these basic units, all other units are defined bymultiplication and division.Thus,all SI units have the following properties:

SI units form a system with state-of-the-art precision: all units are defined with a pre-cision that is higher than the precision of commonly used measurements. Moreover, theprecision of the definitions is regularly being improved.The present relative uncertaintyof the definition of the second is around 10−14, for the metre about 10−10, for the kilo-gram about 10−9, for the ampere 10−7, for the mole less than 10−6, for the kelvin 10−6 andfor the candela 10−3.

SI units form an absolute system: all units are defined in such a way that they canbe reproduced in every suitably equipped laboratory, independently, and with high pre-cision.This avoids as much as possible any misuse by the standard-setting organization.(The kilogram, still defined with the help of an artefact, is the last exception to this re-quirement; extensive research is under way to eliminate this artefact from the definition– an international race that will take a few more years.There are two approaches: count-ing particles, or fixing ħ. The former can be achieved in crystals, the latter using anyformula where ħ appears, such as the formula for the de Broglie wavelength or that ofthe Josephson effect.)

SI units form a practical system: the base units are quantities of everyday magnitude.Frequently used units have standard names and abbreviations.The complete list includesthe seven base units, the supplementary units, the derived units and the admitted units.

The supplementary SI units are two: the unit for (plane) angle, defined as the ratioof arc length to radius, is the radian (rad). For solid angle, defined as the ratio of thesubtended area to the square of the radius, the unit is the steradian (sr).

The derived units with special names, in their official English spelling, i.e., withoutcapital letters and accents, are:

* The respective symbols are s, m, kg, A, K, mol and cd. The international prototype of the kilogram isa platinum–iridium cylinder kept at the BIPM in Sèvres, in France.Page 88 For more details on the levels of thecaesium atom, consult a book on atomic physics.Ref. 323 The Celsius scale of temperature θ is defined as: θ/°C =T/K − 273.15; note the small difference with the number appearing in the definition of the kelvin. SI alsostates: ‘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.’ In the definition of themole, it is understoodthat the carbon 12 atoms are unbound, at rest and in their ground state. In the definition of the candela, thefrequency of the light corresponds to 555.5 nm, i.e., green colour, around the wavelength to which the eyeis most sensitive.* Jacques Babinet (1794–1874), French physicist who published important work in optics.

Motion

Mountain

–The

AdventureofPhysics

pdffileavailable

freeofcharge

atww

w.m

otionmountain.net

Copyright©Christoph

SchillerNovem

ber1997–January2011

348 b units , measurements and constants

monochromatic radiation of frequency 540 ⋅1012 hertz and has a radiant intensity in thatdirection of (1/683) watt per steradian.’ (1979)*

Note that both time and length units are defined as certain properties of a standard ex-ample of motion, namely light. In other words, also the Conférence Générale des Poidset Mesures makes the point that the observation of motion is a prerequisite for the defini-tion and construction of time and space.Motion is the fundament each observation andmeasurements. By the way, the use of light in the definitions had been proposed alreadyin 1827 by Jacques Babinet.*

From these basic units, all other units are defined bymultiplication and division.Thus,all SI units have the following properties:

SI units form a system with state-of-the-art precision: all units are defined with a pre-cision that is higher than the precision of commonly used measurements. Moreover, theprecision of the definitions is regularly being improved.The present relative uncertaintyof the definition of the second is around 10−14, for the metre about 10−10, for the kilo-gram about 10−9, for the ampere 10−7, for the mole less than 10−6, for the kelvin 10−6 andfor the candela 10−3.

SI units form an absolute system: all units are defined in such a way that they canbe reproduced in every suitably equipped laboratory, independently, and with high pre-cision.This avoids as much as possible any misuse by the standard-setting organization.(The kilogram, still defined with the help of an artefact, is the last exception to this re-quirement; extensive research is under way to eliminate this artefact from the definition– an international race that will take a few more years.There are two approaches: count-ing particles, or fixing ħ. The former can be achieved in crystals, the latter using anyformula where ħ appears, such as the formula for the de Broglie wavelength or that ofthe Josephson effect.)

SI units form a practical system: the base units are quantities of everyday magnitude.Frequently used units have standard names and abbreviations.The complete list includesthe seven base units, the supplementary units, the derived units and the admitted units.

The supplementary SI units are two: the unit for (plane) angle, defined as the ratioof arc length to radius, is the radian (rad). For solid angle, defined as the ratio of thesubtended area to the square of the radius, the unit is the steradian (sr).

The derived units with special names, in their official English spelling, i.e., withoutcapital letters and accents, are:

* The respective symbols are s, m, kg, A, K, mol and cd. The international prototype of the kilogram isa platinum–iridium cylinder kept at the BIPM in Sèvres, in France.Page 88 For more details on the levels of thecaesium atom, consult a book on atomic physics.Ref. 323 The Celsius scale of temperature θ is defined as: θ/°C =T/K − 273.15; note the small difference with the number appearing in the definition of the kelvin. SI alsostates: ‘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.’ In the definition of themole, it is understoodthat the carbon 12 atoms are unbound, at rest and in their ground state. In the definition of the candela, thefrequency of the light corresponds to 555.5 nm, i.e., green colour, around the wavelength to which the eyeis most sensitive.* Jacques Babinet (1794–1874), French physicist who published important work in optics.

Motion

Mountain

–The

AdventureofPhysics

pdffileavailable

freeofcharge

atww

w.m

otionmountain.net

Copyright©Christoph

SchillerN

ovember1997–January

2011

348 b units , measurements and constants

monochromatic radiation of frequency 540 ⋅1012 hertz and has a radiant intensity in thatdirection of (1/683) watt per steradian.’ (1979)*

Note that both time and length units are defined as certain properties of a standard ex-ample of motion, namely light. In other words, also the Conférence Générale des Poidset Mesures makes the point that the observation of motion is a prerequisite for the defini-tion and construction of time and space.Motion is the fundament each observation andmeasurements. By the way, the use of light in the definitions had been proposed alreadyin 1827 by Jacques Babinet.*

From these basic units, all other units are defined bymultiplication and division.Thus,all SI units have the following properties:

SI units form a system with state-of-the-art precision: all units are defined with a pre-cision that is higher than the precision of commonly used measurements. Moreover, theprecision of the definitions is regularly being improved.The present relative uncertaintyof the definition of the second is around 10−14, for the metre about 10−10, for the kilo-gram about 10−9, for the ampere 10−7, for the mole less than 10−6, for the kelvin 10−6 andfor the candela 10−3.

SI units form an absolute system: all units are defined in such a way that they canbe reproduced in every suitably equipped laboratory, independently, and with high pre-cision.This avoids as much as possible any misuse by the standard-setting organization.(The kilogram, still defined with the help of an artefact, is the last exception to this re-quirement; extensive research is under way to eliminate this artefact from the definition– an international race that will take a few more years.There are two approaches: count-ing particles, or fixing ħ. The former can be achieved in crystals, the latter using anyformula where ħ appears, such as the formula for the de Broglie wavelength or that ofthe Josephson effect.)

SI units form a practical system: the base units are quantities of everyday magnitude.Frequently used units have standard names and abbreviations.The complete list includesthe seven base units, the supplementary units, the derived units and the admitted units.

The supplementary SI units are two: the unit for (plane) angle, defined as the ratioof arc length to radius, is the radian (rad). For solid angle, defined as the ratio of thesubtended area to the square of the radius, the unit is the steradian (sr).

The derived units with special names, in their official English spelling, i.e., withoutcapital letters and accents, are:

* The respective symbols are s, m, kg, A, K, mol and cd. The international prototype of the kilogram isa platinum–iridium cylinder kept at the BIPM in Sèvres, in France.Page 88 For more details on the levels of thecaesium atom, consult a book on atomic physics.Ref. 323 The Celsius scale of temperature θ is defined as: θ/°C =T/K − 273.15; note the small difference with the number appearing in the definition of the kelvin. SI alsostates: ‘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.’ In the definition of themole, it is understoodthat the carbon 12 atoms are unbound, at rest and in their ground state. In the definition of the candela, thefrequency of the light corresponds to 555.5 nm, i.e., green colour, around the wavelength to which the eyeis most sensitive.* Jacques Babinet (1794–1874), French physicist who published important work in optics.

Motion

Mountain

–The

AdventureofPhysics

pdffileavailable

freeofcharge

atww

w.m

otionmountain.net

Copyright©Christoph

SchillerNovem

ber1997–January2011

Definizione di metro (m)1791: l'Accademia delle scienze francese definisce il metro come 1/10 000 000 della distanza tra polo nord ed equatore, lungo la superficie terrestre, calcolata sul meridiano di Parigi.1889: l'incertezza nella misurazione della distanza portò il Bureau international des poids et mesures (BIPM) a ridefinire nel 1889 il metro come la distanza tra due linee incise su una barra campione di platino-iridio conservata a Sèvres presso Parigi.

1960: con la disponibilità dei laser, l'undicesima Conferenza generale di pesi e misure cambiò la definizione del metro in: la lunghezza pari a 1 650 763,73 lunghezze d'onda nel vuoto della radiazione corrispondente alla transizione fra i livelli 2p10 e 5d5 dell'atomo di kripton-86.1983: la XVII Conferenza generale di pesi e misure definì il metro come la distanza percorsa dalla luce nel vuoto in 1/299 792 458 di secondo (ovvero, la velocità della luce nel vuoto venne definita essere 299 792 458 metri al secondo). Poiché si ritiene che la velocità della luce nel vuoto sia la stessa ovunque, questa definizione è più universale

Ed esistono comunque altre grandezze fisiche fondamentali nel S.I. che verranno introdotte in corsi successivi.

Esistono altre due grandezze fisiche fondamentali nel S.I. che hanno la caratteristica di essere “adimensionali”.

angolo piano angolo solido