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  • I'm here at the National Institute for Standards and Technology, and

  • I'm about to see some of the original kilogram standards. Is that right?

  • Patrick: You are, you are.

  • When were these made?

  • Well the originals were made in the 1880s.

  • There were 40 of them that were brethren of the

  • International prototype kilogram

  • and these 40 were distributed to the signatories

  • of the Treaty of the meter and the

  • United States was given two, K4 and K20.

  • What was this meter agreement?

  • The treaty of the meter?

  • Yeah, what is that?

  • It's the modern-day foundation of the metric system.

  • So the U.S. signed that?

  • The U.S. signed it.

  • As if they were going to become metric?

  • Yes.

  • A little known secret and I'll tell you something else

  • that all the units that we commonly use

  • like feet and gallons and so on are

  • actually defined in terms of metric units.

  • So it's just a little translation

  • that we do here but our country is

  • actually on the metric system.

  • [Laughter]

  • Doesn't that seem crazy?

  • Yes!

  • Isn't that insane that like you base all of these measurements on the metric

  • system and then you add a conversion

  • factor and then later some people have

  • to convert back.

  • Yes, it's stupid.

  • [Laughter]

  • Are you allowed to say that?

  • It's true.

  • So can we see it?

  • sure sure

  • What do we have to do?

  • This requires that we go through

  • some high-security gear and also that

  • would be somewhat clean in what we do

  • so I'll have to ask you to put on some

  • booties here.

  • Let me see if I can do this

  • all right so, did I do it?

  • Yep, there you go.

  • straight back, all the way there you go.

  • This is the first

  • BootieButler that I've ever...

  • I'm a big fan.

  • This is the first layer.

  • Secret code

  • I'm going to show you two I'm going to

  • show you one of the originals and I'm

  • going to show you a more modern version

  • This is K 20.

  • Oh my goodness that is like the

  • original kilogram mass standard of the US.

  • That's right.

  • I never thought I would

  • get this close to it

  • virtually every mass that has been

  • accurately weighed in the US over the

  • past hundred and thirty years can trace

  • its measurement back to this one

  • kilogram hunk of 90 percent platinum 10 percent iridium.

  • Iridium makes the alloy much

  • harder than pure platinum and both

  • elements were selected for their high

  • density and resistance to oxidation this

  • kilogram was created in the same way at

  • around the same time as an object which

  • to this day remains the definition of

  • the kilogram an identical cylinder

  • stored in a basement vault on the

  • outskirts of Paris.

  • If you look straight

  • down from the top you can maybe see K 20

  • doesn't have a very nice finish on it

  • compared to the more modern prototypes

  • here's K 92 so it's got a much higher

  • polish on it different manufacturing

  • techniques absolutely no swirls it is a

  • really like beautiful looking specimen

  • yes it is I mean is there a reason why

  • you want it to look so beautiful?

  • well you want it not to be very rough

  • because roughness increases surface area

  • surface area increases the probability

  • that you will get contaminants on that

  • will change the mass of the entire thing

  • how much is it worth

  • well monetarily the new ones are about

  • $100,000 a piece if you were to buy one

  • oh my goodness so but if you think about

  • K 20 K for with about 130 years of

  • history they're priceless you could

  • never replace them the purpose of this

  • room then is to share the precise mass

  • of K 20 with anyone who wants to make a

  • measurement without sharing K 20 itself

  • what we do in this suite here is we

  • transfer the definition of the kilogram

  • from the platinum-iridium prototypes to

  • stainless steel secondary standards and

  • you can tell that they're a lot bigger

  • and the platinum-iridium prototypes and

  • that's because of the relative

  • difference in density the density of

  • stainless steel is about 8 grams per

  • cubic centimeter whereas the density of

  • platinum iridium is about 21.5 grams per

  • cubic centimeter so there's all of the

  • three times difference in density which

  • tells you why this is so much bigger in

  • volume and that creates a problem

  • ordinarily we don't worry much about the

  • buoyant force that is the upward force

  • on every object in the atmosphere equal

  • to the weight of air it displaces but

  • since the volumes of these masses are so

  • different a stainless steel object that

  • has around the same mass as k20 can have

  • its weight reduced due to buoyancy by

  • around 110 milligrams

  • the precise amount depends on the

  • temperature pressure and humidity of the

  • air that's why the mass comparator

  • itself is inside of a chamber here

  • that's isolated from the outside world

  • so that the temperature remains

  • relatively stable I'm the humidity the

  • same pressure is by far the biggest

  • contributor to air density so we don't

  • want it changing all over the place with

  • the weather the problem scientists are

  • having with the kilogram now is much

  • bigger than weather fluctuations it's

  • something they discovered when all the

  • original kilograms were returned to

  • Paris for a weigh-in including k20 how

  • did it get there it gets there by a

  • person hand carrying it each prototype

  • gets taken out of the bell jar and put

  • in its container how do we sound after

  • we get it in there all nicely secured

  • then we wrap the whole thing in bubble

  • wrap and put it in a camera bag and

  • sling it over our shoulders don't let it

  • out of our sight it sounds a little

  • casual so you actually like while you're

  • on the plane do you put it in like the

  • overhead stretch

  • know it stay just at all times like it's

  • a you know the nuclear football codes

  • were setting off a nuclear weapon and

  • you never have any scares while you're

  • carrying the only scare comes that

  • somebody wants to see it like a customs

  • official I've never had to open it

  • although I had a kind of a scary moment

  • at one time when they asked me what it

  • was made of and I told them it was

  • platinum iridium and somebody heard the

  • word iridium and connected that with

  • radioactivity no no and kind of you know

  • flew off the handle a little bit and I

  • had to calm them down on the shoreland

  • that it wasn't radioactive there was no

  • threats going on here

  • the real threat was the unreliable

  • weight and the kilogram mass standard

  • what they do is a series of comparisons

  • they compare every one of those with the

  • International prototype kilogram using

  • that data and plotting it it looked as

  • if there had been a change in the

  • International prototype that made it

  • about 50 micrograms heavier than one

  • kilogram now over the course of a

  • hundred years all right

  • but the interesting thing is if one

  • looks at the data that was recently

  • taken at the end of 2013 international

  • prototype kilogram did not show an

  • increasing mass telling me for several

  • decades it was gaining mass and also on

  • the stop which you know I find that hard

  • to explain but it seemed like all of the

  • 40 masses in to be somewhat diverging at

  • that weigh-in they went different ways

  • they went in different directions yes so

  • that some changed a lot some changed

  • little some hardly changed at all but

  • it's hard to tell I mean they could

  • we'll all be changing a lot but because

  • all you can tell is the difference

  • between them they've already married

  • all that matters is the difference

  • between them and the International

  • prototype because the International

  • prototype is the only thing you need the

  • only thing that you really know because

  • it's defined as one kilogram

  • right but I mean the outside of that

  • definition there's a chance it could

  • have gained you know five grams as long

  • as they all gain five grams you know I'm

  • having these ridiculous obviously it's

  • ridiculous but the point is they could

  • have all been gaining or they could all

  • been losing right it's a relative

  • measurement and that's the weakness of

  • the system

  • and that's why as of 2018 the kilogram

  • will no longer be defined as the mass of

  • a metal cylinder why if you want to find

  • out how the kilogram will be redefined

  • be sure to subscribe to Veritasium

I'm here at the National Institute for Standards and Technology, and

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B1 中級

アメリカは実はメートル法なのか? (Is America Actually Metric?)

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    林宜悉 に公開 2021 年 01 月 14 日
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