O História of o Kilogram
De Platinum to Quantum Física
Experimente Peso ConversorFor 130 years, o mundo's definition of a kilogram depended on a single object: a small cylinder of platinum-iridium alloy locked in a vault outside Paris. Todo scale, todo weight medição, todo kilogram on Earth foi ultimately compared to este one artifact. Então, in 2019, everything changed.
O story of o kilogram é a remarkable journey through o história of medição—from o chaos of pre-revolutionary France to o cutting edge of quantum física.
Before o Kilogram: Medição Chaos
Before o métrico sistema, weight medição foi a nightmare. Todo town, todo trade, e todo country had its own standards. A "pound" in Paris wasn't o mesmo as a pound in Lyon. Merchants faced constant confusion, e opportunities for fraud foram rampant.
O French Revolution, com its ideals of equality e rationality, provided o perfect opportunity for reform. In 1790, o National Assembly charged o French Academy of Sciences com creating a universal sistema of medição based on nature, not royal decrees ou local customs.
O Birth of o Kilogram (1795-1799)
O novo sistema needed a unidade of mass. Scientists decided it should be o mass of one cubic decimeter (one liter) of water at its densest temperature (sobre 4°C). They called este unidade o "grave," later renamed o "kilogramme."
But water é impractical as a padrão—you can't ship a liter of water around o mundo e expect it to stay o mesmo. So in 1799, a physical artifact foi created: a cylinder of pure platinum esse matched o mass of a liter of water as closely as possible. Este became o primeiro official kilogram padrão.
“O kilogram é o unidade of mass; it é igual to o mass of o international prototype of o kilogram.”
O International Prototype Kilogram (1889)
As o métrico sistema spread globally, nations needed a shared padrão. In 1889, o International Bureau of Weights e Measures (BIPM) created o International Prototype Kilogram (IPK)—a cylinder of 90% platinum e 10% iridium, sobre 39 millimeters in diameter e height.
O IPK foi stored in a climate-controlled vault at o BIPM headquarters in Sèvres, France, under three nested bell jars. Forty copies foram distributed to nations worldwide as national standards. And for 130 years, by definition, este cylinder WAS a kilogram—not aproximadamente, but exatamente.
O Problem com Physical Standards
But lá foi a problem. Quando scientists periodically compared o national copies to o IPK, they found o copies had drifted in mass relative to cada outro—by sobre 50 micrograms over a century. Was o IPK gaining mass (from contamination) while copies stayed constant? Were o copies changing? Lá foi no way to know because o IPK foi o definition itself.
O 2019 Revolution: Planck Constant Definition
Scientists had long wanted to redefine o kilogram in terms of fundamental constants of nature—values esse don't change over time. After decades of precision experiments, they succeeded.
On May 20, 2019, o kilogram foi redefined based on o Planck constant (h), a fundamental value in quantum mechanics. O definition agora fixes o Planck constant at exatamente:
h = 6.62607015 × 10⁻³⁴ joule-seconds
Through o relationship entre mass, energy, e Planck's constant, este defines o kilogram in terms of an unchanging natural constant. O IPK é ainda kept in Paris, but it's agora apenas a muito precise 1-kilogram weight, not THE kilogram.
Timeline of Key Events
| Year | Event | Significance |
|---|---|---|
| 1790 | French Academy begins work on métrico sistema | Foundation of modern medição |
| 1795 | Kilogram definido as mass of 1L water | Primeiro definition |
| 1799 | Platinum kilogram padrão created | Primeiro physical artifact |
| 1875 | Metre Convention signed | International medição cooperation |
| 1889 | IPK becomes mundo padrão | Platinum-iridium cylinder |
| 1901 | Massa vs weight distinction clarified | Scientific precision |
| 2011 | Redefinition work approved | Planck constant approach chosen |
| 2019 | Novo definition takes effect | Based on fundamental constants |
Por que It Matters
O novo definition might seem like an academic concern, but it tem prático implications:
- Stability: O definition can never drift ou change over time
- Reproducibility: Qualquer laboratory can theoretically realize o kilogram, not apenas o BIPM
- Precision: As medição technology improves, o kilogram can be realized mais precisamente sem changing o definition
- Independence: No single artifact controls mundo medições
O kilogram foi o último SI unidade definido by a physical artifact. Agora todos seven base unidades são definido by fundamental constants—a triumph of precision ciência.
Conclusão
De a liter of water in revolutionary France to o quantum mechanics of o Planck constant, o kilogram's história reflects humanity's quest for ever-greater precision. O 2019 redefinition ensures esse future generations won't depend on a single metal cylinder in a Parisian vault but on o unchanging constants of nature itself.