kilogram kilogram unit symbol base unit mass metric system defined equal mass known big kilogram defined mass cubic centimeter water melting point ice final kilogram manufactured prototype derived mass equal mass water maximum density approximately base unit prefix symbol unit directly defined artifact fundamental physical property reproduced different laboratories base units derived units system defined relative kilogram stability important units require kilogram definition temperature time frequency length angle commissioned authority custody hold behalf found vary mass time relative recommended kilogram terms fundamental constant nature meeting agreed principle kilogram terms constant decision originally deferred deferred meeting currently different proposals abandoned described section rarely handled copies kept national laboratories world compared provide measurements mass world international pound imperial customary systems defined exactly making kilogram approximately equal pounds traditional units weight mass world defined terms kilogram making primary standard virtually units mass earth terminology word kilogram derived french learned greek stem thousand late latin term small weight greek word written french law decree revised older system units introduced defined weight cubic water equal grave decree term replaced replaced grave french spelling adopted united_kingdom word time english spelling kilogram adopted united_states united_kingdom kilogram having far common law regulating units trading weight measure prevent use spelling 19th century french word shortening imported english language mean kilogram kilometer acceptable texts example economist use typically considered inappropriate certain applications including scientific technical legal writing authors adhere strictly nomenclature united_states congress gave metric system legal status permitted use word alternative word kilogram revoked status word 19th century standard system metric units second system units treating fundamental unit mass kilogram simply derived unit following discoveries effect electric measurements explained terms fundamental units length mass time proposed new standard system include fourth fundamental unit measure quantities adopted system known system approved proposal adopt electromagnetic unit system commissioned recommendations single practical system units measurement suitable adoption countries metre convention led launch subsequent publication stated use unit symbols unit names systems existed early mid 20th century result decision adopt system international system units kilogram base unit mass definition derived kilogram nature mass kilogram unit mass property corresponds common perception heavy object mass property related tendency object rest remain rest motion remain motion constant velocity acted force according newton laws motion equation second law motion acted force newton object mass kilogram accelerate rate meter second second tenth acceleration earth gravity weight object dependent strength local field mass object independent gravity mass measure matter object contains accordingly effort required hold objects cabin floor objects retain mass astronaut exert times force accelerate kilogram object rate kilogram object given point earth weight object proportional mass mass object kilograms usually measured comparing weight weight standard mass mass known kilograms device called weighing scale ratio force gravity objects measured scale equal ratio masses april decreed france absolute weight volume pure water equal cube metre temperature melting ice concept unit volume water define unit measure mass proposed english philosopher essay means linking mass length trade commerce typically involve items significantly massive mass standard water unstable regulation commerce necessitated manufacture practical realization water based definition mass accordingly provisional mass standard single piece metallic artifact thousand times massive kilogram time work commissioned precisely determine mass cubic water decreed definition kilogram specified water highly stable temperature point french chemist italian naturalist years research chose standard water stable density point temperature water reaches maximum density measured time concluded cubic water maximum density equal target mass provisional kilogram standard years earlier year platinum kilogram prototype fabricated objective equal close scientifically feasible day mass cubic water prototype presented june december prototype formally ratified des archives kilogram archives kilogram defined equal mass standard stood years international prototype kilogram magnitude kilogram defined mass object called international prototype kilogram referred professional world platinum known platinum mass right circular cylinder height diameter millimeters minimize surface area addition improved platinum kilogram archives greatly increasing retaining platinum virtues extreme resistance extremely high density twice dense lead times dense water satisfactory electrical thermal low magnetic sister copies stored known french language initials environmentally monitored safe lower vault located basement outskirts paris external images photographs independently controlled keys required open vault official copies available nations serve national standards compared roughly years providing local measurements signed metric system predecessor quickly leading production cylinders continues manufacture nearly national prototypes today mass found indistinguishable eighty years prior formally ratified kilogram 1st modern measurements vienna standard mean ocean water pure water composition representative average world oceans density point maximum density standard atmosphere pressure cubic water point maximum density parts million massive difference shows scientists years ago managed mass kilogram archives equal cubic water margin error mass single excess grain rice copies international prototype kilogram copies international prototype kilogram given following designations literature located france sister copies numbered located france unofficial copies numbered numbers replaced located france national prototypes stored australia austria belgium brazil canada china hong_kong czech_republic denmark egypt finland france germany hungary india indonesia israel italy japan kenya mexico netherlands north_korea norway pakistan poland portugal romania russia serbia singapore slovakia south_africa south_korea spain sweden switzerland taiwan thailand turkey united_kingdom united_states additional copies held non national organizations paris stability international prototype kilogram definition error measured value mass exactly zero kilogram changes mass time comparing mass official copies stored world rarely undertaken process called periodic occurred instance owns platinum kilogram standards original batch delivered prototype designated primary national standard mass nations periodically returned note mass precisely equal masses documented offset values instance primary standard originally official mass performed showed mass latest performed shows mass precisely identical original value unlike variations check standard declined mass relative identifiable reason check standards primary standards prone wear originally delivered official mass officially years later period years lost relative simple wear check standards experience mass carefully stored national prototypes drift relative variety reasons known unknown stored air albeit bell gain mass atmospheric contamination surfaces accordingly cleaned process developed known cleaning method comprises firmly soaked equal parts followed steam cleaning water allowing prototypes settle days cleaning prototypes removes contamination depending largely time cleaning second cleaning remove cleaning stored bell immediately begin gaining mass developed model gain concluded averaged month months cleaning decreased average year check standards like cleaned routine mass standards precaution minimize potential wear handling damage model time dependent mass gain cleaning correction factor official copies stored similar conditions periodic large number especially national primary standards rarely convincingly demonstrate stability clear periodic performed masses entire worldwide ensemble prototypes slowly clear mass lost century possibly significantly comparison official copies reason drift dedicated careers unit mass plausible mechanism proposed explain steady decrease mass increase dispersed world relative nature changes world kilogram prototypes popular press notable scientific magazines state simply lost important comparison official copies technical means available determine entire worldwide ensemble prototypes suffers greater long term trends upwards downwards mass relative nature unknown level period years given lack data identifying world kilogram prototypes stable absolute terms equally valid state batch group gained average years comparison known specifically exhibits short term instability period month cleaned mass precise reason short term instability understood thought surface effects microscopic differences prototypes polished surfaces possibly aggravated hydrogen absorption volatile organic compounds slowly deposit prototypes based clean possible rule explanations observed masses world prototypes proposed scientists general public explains example divergence dependent time measurements dependent number times artifacts cleaned possible changes gravity environment reports published based ray samples stored alongside prototype kilograms suggested source divergence prototypes traced mercury absorbed prototypes proximity mercury based instruments stored centimeters mercury far late 1980s work platinum weights nineteenth century found mercury surface contaminated equivalent mercury scaled surface area kilogram prototype scientists seeing far greater prototypes previously believed increasing divergence masses world prototypes short term instability prompted research improved methods obtain smooth surface finish diamond turning newly manufactured intensified search new definition kilogram proposed future definitions stability crucial kilogram system measurement currently defined structured instance newton defined force necessary accelerate kilogram meter second squared mass change slightly newton proportional degree turn unit pressure defined terms newton chain follows units measure instance unit energy defined expended force newton acts meter affected unit power second defined relative newton ultimately kilogram magnitude primary units electricity determined kilogram follow units measure light affected following change turn affect magnitude units comprising system measurement ultimately defined mass year old golf ball sized piece metal quality protected preserve integrity system despite best average mass worldwide ensemble prototypes mass likely diverged periodic years ago world national laboratories wait fourth periodic confirm historical trends persisted fortunately definitions units different practical instance meter defined distance light travels vacuum time interval second meter practical realization typically takes form neon laser meter length defined light laser suppose official measurement second found drifted parts billion actually extremely stable parts automatic effect meter second meter length laser comprising meter practical realization scientists performing meter simply continue measure number laser agreement reached true regard real world kilogram mass found changed slightly automatic effect units measure practical provide layer eventually reconciled virtue system precise mathematical logical harmony units value definitively proven changed solution simply kilogram equal mass plus offset value similarly currently kilogram equal mass parts billion equivalent long term solution problem liberate system developing practical realization kilogram reproduced different laboratories following written specification units measure practical realization precisely defined expressed terms fundamental physical major portions system based kilogram kilogram turn based universal nature work end ongoing alternative achieved uncertainty parts billion required improve april implementation balance approaching goal demonstrated uncertainty balance pound imperial customary systems defined exactly making kilogram approximately equal pounds proposed future definitions following sections shown form denote uncertainty standard confidence level significant final proposed definition denotes agreed kilogram unit defined artifact meter having previously defined reference artifact single platinum bar marks terms fundamental physical particular light emitted later speed light standard reproduced different laboratories following written specification meeting international committee weights measures recommended kilogram october voted submit resolution consideration note intention kilogram defined terms constant dimensions energy times time fundamental units resolution accepted 24th conference october addition date 25th conference moved forward definition theoretically permit apparatus capable kilogram terms constant long possessed sufficient precision accuracy stability balance discussed able project replace artifact variety different technologies approaches considered explored years covered abandoned approaches based equipment procedures enabled production new kilogram mass prototypes demand albeit extraordinary effort measurement techniques material properties ultimately based fundamental based devices measured acceleration weight hand tuned kilogram test masses expressed electrical terms special components permit fundamental approaches depend converting weight measurement mass require precise measurement strength gravity laboratories approaches precisely fixed nature defined value balance balance essentially single pan weighing scale measures electric power necessary oppose weight kilogram test mass pulled earth gravity variation balance employs extra step effect geometry electric potential balance voltage standard allows voltage linked constant nature extremely high precision stability circuit resistance quantum hall resistance standard balance requires precise measurement local acceleration laboratory absolute external images instance earth gravity gradient meter elevation center differs nearby test mass balance change weight kilogram test mass april implementation balance demonstrated combined relative standard uncertainty short term resolution balance demonstrated balance shipped canada research development device continue adopts new proposal new definition kilogram value units constant measure relates energy frequency precisely fixed currently accepted value uncertainty million agreed internationally kilogram longer defined mass remaining units today kilogram fall place ultimately defined terms gravity nature balance test masses local acceleration exploited mechanical power compared electrical power square voltage divided electrical resistance varies significantly nearly depending earth surface measurement earth gravity slight seasonal variations changes underground water tables larger changes tidal earth shape caused moon term definition kilogram crucial kilogram relating energy power accordingly measured precision accuracy terms measurements fundamental nature precise work mass measured dropping mass absolute contain stabilized neon laser fringe signal frequency sweep output measured atomic clock type dropping mass derives accuracy stability speed light innate properties neon gravity term electronic kilogram measured terms nature high precision instance basement facility measuring gravity acting test masses smaller slightly lower center gravity inside balance steel masses measured value typically virtue electronic like balance definition kilogram longer dependent stability kilogram prototypes carefully handled stored free need rely assumptions stability prototypes instead hand tuned close mass standards simply weighed documented equal kilogram plus offset value balance kilogram electrical gravity terms nature defined manner directly fundamental nature constant defines kilogram terms second meter fixing constant definition kilogram depend definitions second meter definition second depends single defined physical constant ground state splitting frequency meter depends second additional defined physical constant speed light kilogram manner mass artifacts physical objects balance including longer definition instead transfer standards scales like balance permit flexibility choosing materials especially desirable properties mass standards instance continue specific gravity newly produced mass standards existing national primary check standards reduce relative uncertainty making mass comparisons air alternatively entirely different materials constructions explored objective producing mass standards greater stability instance investigated platinum absorb hydrogen based cleaning atmospheric mercury proved sources instability deposited protective like investigated new challenge reducing uncertainty making truly practical kilogram nearly aspect support equipment requires precise accurate state art technology unlike device like atomic clock countries currently choose fund operation instance balance resistance standards rotated balance weeks different headquarters facility maryland found simply moving resistance standards hall balance altered values equivalent present day technology insufficient permit stable operation kilogram defined terms constant likely initially operating world alternative approaches kilogram fundamentally different balance explored varying degrees abandoned follows counting approaches offering practical realization definition precisely define magnitude kilogram terms certain number carbon carbon carbon mole currently defined quantity entities elementary particles like molecules equal number grams carbon current definition mole requires mass precisely kilogram number mole quantity known constant determined current best estimate value entities mole new definition kilogram proposed fix constant precisely kilogram defined mass equal accuracy measured value constant currently limited uncertainty value constant measure relating energy frequency relative standard uncertainty parts billion fixing constant practical effect proposal uncertainty mass magnitude kilogram better current uncertainty constant proposal magnitude kilogram subject future improved measurements value constant available electronic kilogram required conversely electronic definition kilogram electronic approaches precisely fix constant continue allow mass precisely kilogram number comprising mole constant continue subject future variation based definition proposes define constant precisely imaginary realization mass prototype cube measuring precisely proposal kilogram defined mass equal project constant based approach known project define kilogram size diameter sphere chosen commercial infrastructure mature processes creating defect free ultra pure exists service industry practical realization kilogram rod like single crystal produced composition measured mass determine average relative atomic mass cut ground polished spheres size select sphere measured optical uncertainty radius roughly single atomic layer precise crystal structure measured scanning ray permits atomic determined uncertainty parts billion size sphere average atomic mass atomic known required sphere diameter calculated sufficient precision low uncertainty enable finish polished target mass kilogram experiments performed project spheres determine masses stable stored vacuum partial vacuum ambient pressure technical means currently exist prove long term stability better sensitive accurate measurements mass dual pan like strip balance external links compare mass sphere reference mass given latest understanding lack long term mass stability known perfectly stable mass artifact compare single pan scales measure weight relative nature precise necessary long term uncertainty parts billion issue overcome forms thin layer equivalent dioxide layer slightly increases mass sphere effect accounted sphere finished dimension issue platinum noble metals roughly oxygen don laboratory presence thin layer sphere mass prototype places additional restrictions procedures suitable clean avoid changing layer thickness based approaches fix constant vary details definition kilogram approach use natural present comprises heavier described carbon method define magnitude kilogram terms certain number fixing constant sphere practical realization approach accurately magnitude kilogram masses relative known great precision relative better alternative method creating sphere based kilogram proposes use separation techniques nearly pure relative atomic mass approach constant fixed atomic mass definition kilogram kilogram instead defined fixed elect define kilogram terms kilogram prototypes natural present kilogram definition based theoretically pure sphere prototype nearly pure necessarily slightly defined number compensate chemical effect surface accumulation based approach accumulation abandoned defined kilogram precisely creating new metal prototypes demand accumulating gold stripped electron counted measuring electric current required gold chosen safely handled highest atomic masses elements effectively non radioactive perfectly stable gold table gold based definition kilogram instance relative atomic mass gold fixed precisely current value definition based carbon constant fixed kilogram defined mass equal precisely gold precisely gold fixed german experiments gold current demonstrated relative uncertainty follow experiments current expected accumulate mass days relative uncertainty better ultimately accumulation approaches proved unsuitable measurements required months data proved erratic technique considered viable future replacement technical challenges deposition apparatus obtaining sufficiently high current mass deposition rate simultaneously deposit target embedded balance pan experiments gold showed low energies avoid effects phenomenon counted target deposited deposited mass fraction german experiments approached close energies gold kilogram defined precise quantity gold deposited electric current constant atomic mass gold precisely fixed value elementary charge likely currently recommended value effectively defined flow second past fixed point electric circuit unit mass fully defined having precisely fixed values constant elementary charge exploiting fact atomic masses gold universal nature making new mass standard poor shortcomings accumulation approach proved formidable obstacles accumulation based techniques practical realization apparatus necessarily required deposition chamber integral balance system enable convenient reasonable quantity transfer standards relative single internal deposited prototype furthermore mass prototypes produced deposition techniques like platinum prototypes currently use deposited pan special balance integrated device deposited mass wouldn hard highly polished surface vigorously cleaned like current prototypes gold dense noble metal resistant formation compounds extremely soft internal gold prototype kept isolated clean avoid contamination potential wear having remove contamination inexpensive metal low temperature slowly exposed room temperature air forms chemical compounds produced stable reference masses continually maintained vacuum atmosphere based force approach define kilogram mass accelerated precisely subjected meter force straight parallel infinite length circular cross section placed meter apart vacuum flow constant current elementary charges second effectively define kilogram derivative present relationship defines derivative kilogram kilogram specify elementary charge precisely current recommended value necessarily follow second electric current precise quantity elementary charges second passing given point electric circuit virtue practical realization based definition unlike balance scale based methods require careful characterization gravity laboratory method magnitude kilogram directly terms define nature mass acceleration applied force unfortunately extremely difficult develop practical realization based accelerating masses experiments period years japan mass supported achieved uncertainty better parts million magnetic limiting issues groups performed similar research different techniques mass linked symbol unit measure kilogram prefix instance kilogram typically abbreviated supplement avoid confusion prefix recognized outside technical disciplines expression symbol obsolete unit measure known equal medication errors confusion abbreviated recommendation given expressed word written acceptable use europe abbreviated local spelling typical retail quantities food cheese meat unit rarely typically technical fields contexts especially rigorous consistency standard desired purposes instead symbol adopted unit accepted use according english speaking countries unit usually called metric ton unit general interest literature greenhouse gas emissions equivalent unit scientific papers subject isolated effect changed form simplified accessible process artifact simple human object directly comparative standard measurement physical quantity check standard standard body backup replica international prototype kilogram secondary kilogram mass standard stand primary standard routine definition formal specific exact specification physical means mark boundary express magnitude entity widely distribute magnitude unit measure typically transfer standards international prototype kilogram unique physical object kept france internationally recognized having defining mass precisely kilogram magnitude extent value property national prototype replica possessed nation practical realization readily apparatus magnitude unit measure primary national standard replica possessed nation replica nation possesses prototype human object serves defining comparative standard measurement physical quantity human object serves comparative standard measurement physical quantity replica official copy sister copy official copies stored safe check standards transfer standard artifact apparatus magnitude unit measure different usually practical form
Kilogram