科學(xué)60秒:質(zhì)量標(biāo)準(zhǔn)，不標(biāo)準(zhǔn)
來源：滬江聽寫酷
2011-07-08 10:00
In a laboratory vault outside Paris is a small cylinder of platinum–iridium alloy that ___1___ the standard for all mass measurements worldwide. By an 1889 international accord, the mass of this metal cylinder defines the kilogram.
But that may soon change. The kilogram is the only unit of measurement still based on a ___2___. A second of time, for instance, is now defined in terms of an electron transition of the cesium atom. And ___3___. Those standards are universal and unchanging—unlike the official kilogram. The reference cylinder's mass has ___4___ through the years—not enough to throw off your bathroom scale, but enough to bother measurement scientists.
Some of them are meeting January 24th at the Royal Society in London to discuss future improvements to the measurement units. The plan is to eventually relate the kilogram to a universal number known as Planck's constant. But the technology needed to do that is not yet fully developed. So, for the time being, that little metal cylinder outside Paris will just have to ___5___. I mean, mass.
【視聽版科學(xué)小組榮譽出品】
But that may soon change. The kilogram is the only unit of measurement still based on a ___2___. A second of time, for instance, is now defined in terms of an electron transition of the cesium atom. And ___3___. Those standards are universal and unchanging—unlike the official kilogram. The reference cylinder's mass has ___4___ through the years—not enough to throw off your bathroom scale, but enough to bother measurement scientists.
Some of them are meeting January 24th at the Royal Society in London to discuss future improvements to the measurement units. The plan is to eventually relate the kilogram to a universal number known as Planck's constant. But the technology needed to do that is not yet fully developed. So, for the time being, that little metal cylinder outside Paris will just have to ___5___. I mean, mass.
【視聽版科學(xué)小組榮譽出品】
serves as man-made artifact the meter is tied to the speed of light drifted slightly keep pulling its weight
巴黎城外的一個玻璃罩里存放著一個鉑銥合金圓柱體，這個圓柱體就 是全世界測量物體質(zhì)量的參照標(biāo)準(zhǔn)。1889年某項國際協(xié)議中規(guī)定，該 鉑銥合金圓柱體的質(zhì)量為1千克。 但這個標(biāo)準(zhǔn)即將成為過去。千克是目前唯一一個以人工制品為參照標(biāo) 準(zhǔn)的計量單位。比如說，秒就是根據(jù)銫原子內(nèi)部的電子躍遷時間來的 下定義，而米的定義則和光速有關(guān)。這些計量標(biāo)準(zhǔn)普遍通用、亙古不 變，而千克的參照標(biāo)準(zhǔn)則不然。歷經(jīng)多年，質(zhì)量標(biāo)準(zhǔn)參照物——鉑銥 合金圓柱體的質(zhì)量已略有減輕。你倒不至于把浴室秤給扔掉，但計量 學(xué)家就有得操心了。 部分計量學(xué)家將于1月24日在英國皇家學(xué)會舉行會議探討計量標(biāo)準(zhǔn)的改 善問題，計劃最終將千克這個計量單位與普朗克常數(shù)聯(lián)系起來。然而 ，要完成這項工作，技術(shù)問題仍有待解決。因此，在此之前，那小小 的合金圓柱體還得繼續(xù)扮演“重量”級的角色，當(dāng)然，是在質(zhì)量測量 方面的重量級角色。
