Metrum

Haec pagina de longitudine explicat. Si quid quaeris quod et "Metrum" appellatur, vide Metrum (discretiva).

Metrum ordiale, Platinum-Iridium. Definitio metri usque ad annum 1960.

Metrum (-i, n.) (Graece: μέτρον, via Francogallice mètre) est mensura principalis (Anglice: base unit) longitudinis, una ex septem principalibus physicae mensuris in Internationali Unitarum Systemate (Anglice: International System of Units). Definitio, primum excogitatum ut 10 000 000 pars spatii ab aequatore ad Polum Septentrionalem, continenter expolitur ut auctum metrologiae scitae implicet. Post 1983, metrum definitur ut spatium a luce in vacuo transitum 299 792 458 parte secundi.

Definitio

Vetus

Anno 1793 metrum primum definitum fit. Definitio erat metrum esse partem $1/40000000$ meridiani orbis, qui Lutetiam percurrit. Anno 1795 primum exemplar in metallo orichalco factum et anno 1799 exemplar finale, quod "metrum ordiale" nominatur, in metallo platino funditum est.

Mensurae magis exactae telluris in saeculo undevicensimo effectae monstrabant priorem mensuram falsam fuisse. Novum exemplar necessarium erat. Hoc anno, 1889, ab officiis mundi ponderum et mensuris in metallis platino (90%) et iridio (10%) funditum est.

Ab anno 1960 usque ad annum 1983 metrum erat pars producti $1650763,73$ longitudinis undae in vacuo quae atomus Cryptonis-86 inter affectiones 5d5 et 2p10 mutans generat.

Hodierna

Ab anno 1983, metrum definitur ut spatium quod lumen in vacuo in parte $1/299792458$ secundi percurrit, ut velocitas lucis subtiliter definita sit sequenti modo

$c = 299792458 \;\mathrm{m}/\mathrm{s}$

Variae Longitudines

chiliometrum = 1000 metrorum

decimetrum = 1/10 metri

centimetrum = 1/100 metri

millimetrum = 1/1000 metri

micrometrum (micron) = 1/1 000 000 metri

nanometrum = 10^-9 metri

picometrum = 10^-12 metri

femtometrum = 10^-15 metri

Vide etiam

• Index magnitudinum physicarum
• Spatium

Bibliographia

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