They are the same. Even a pound of steel and a pound of feathers. But a pound of gold and a pound of feathers aren't. Well, an ounce of gold and an ounce of feathers aren't. Because an ounce of gold is a Troy ounce. (An old joke. When Troy pound existed, a pound of feathers was heavier.)
So apparently the new kilogram standard is this - "The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10-34 when expressed in the unit J s, which is equal to kg m2 s -1 , where the meter and the second are defined in terms of c and ∆νCs."
This is neat. Doesn't tell us how they'll actually 𝘮𝘦𝘢𝘴𝘶𝘳𝘦 kilograms for standardisation purposes, but the definition itself is pleasingly simple and universal. Yes, I said simple. If you don't believe me, try these two on for size: "The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s-1." "The candela, symbol cd, is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 x 1012 Hz, Kcd, to be 683 when expressed in the unit lm W-1, which is equal to cd sr W-1, or cd sr kg-1 m-2 s3, where the kilogram, metre and second are defined in terms of h, c and ΔνCs." See my point? 😉
@@theJuggla17 Fahrenheit is defined based on kelvin, and "since 2019 the scale has been defined by fixing the Boltzmann constant k to be exactly 1.380649×10−23 J⋅K−1."
A channel that has 1.62M subs in 2020 had a comment with just 1 like for 4 Years! UA-cam really is the level playing field one hopes for! Hey Grady! Love Your videos!! One of my favourite channels out there!!
And today 16.11.2018 The vote to change the definition of the kilogram has offically and unanimously passed in paris. SI-Units will no longer depend on physical artifacts, just on the fundamental constants of nature. Praise Science
Funny thing here, the new definition of the kilogram came into effect on the day of my physics exam, and the examinations removed a question regarding the definition, because the answer didn't hold up anymore.
I am from the future. The kilogram is now defined based on the Planck constant, which is absolute, universal, and has units of kilogram meters-squared per second. With the physically defined meter and second, this number can be used to define a kilogram.
@@marielikes2502 yes, but the reason why MrLagEveryP2WServer was confused was because it looks like the guy in the background is doing things on top of it.
"Operation Gram Slam, Mr. Bond is where my team of svelt cat burglars shave milligrams off *the* Kilogram thus increasing the amount of all my stuff. Ha ha!" "But wouldn't that increase everyone's stuff equally, Gramfinger?" "oh .. yeah."
There was an attempt to standardize kilogram as a liter of water at 0°C and under atmospheric pressure, but the problem as, that pressure units are derived from are and mass, so it would refer to itself.
I worked for the Metrology Lab at NMSU it was pretty cool. It was kind of weird because we got a lot of shipments from all over New Mexico to validate their weight… it's kind of weird when it's like, “Package weight: 1 kg ± 5 µg” Apparently, there's a set of weights that keeps getting posted around to the various state metrology labs and they weigh them and compare results. It was kind of cool. :)
I briefly worked at the International Bureau of Weights and Measurements, at the masses department, I could have a glance at the Kibble scale, that machine made to correlate the kilogram to the Planck constant so we don't rely on standard masses anymore. That thing is so precise it can catch the gravitational gradient across the room. Heck it even has to take into account its own gravitational field in the computation. They put it in in a basement room after removing the floor, so it has no physical contact with the building.
Well explained tom. I find metrology is a subject people either click with instantly or just seem puzzled by the whole thing all together. Good concise explanations of some quite complicated information. NPL have excellent training information too so good to see they have a channel, thanks
The watt balance thing is amazing! That is definitely the most practical way of doing it, though there is more room for error in execution that won't result in an obvious failure.
Surely the main problem with it is that gravity isn't constant around the world, whereas the kilogram is a unit of mass and needs to be independent of such things?
For the majority of the world gravity is considered to be constant as the relative height differences between different counties compared to the radius of the earth is most of the time insignificant. But for the absolute 1 kg mass it would make a difference. So how about using the watt balance at agreed radius from the centre of the earth so that gravity would be constant and the weight of a 1 kg mass would also be the same.
Wilron Gravity isn't constant even at constant radius from the centre of the Earth--local geology can make a difference. Not a large difference, but when you want something to be accurate to better than a millionth of a percent, an important difference. Also, how would you accurately measure your distance from the centre of the Earth in the first place?
+Tom Scott, you should do a video at the The National Museum of Computing at Bletchley Park. Just when I thought I was fully geeked out, I turned around and saw the slide rules....
This is actually strangely relevant to me right now, as I'm doing some worldbuilding, and trying to figure out some mathematical constants for my universe.
Having been to the NPL I can confirm its an amazing place, they have the darkest room in Europe there, as well as an insanely cool anechoic chamber. As an aside, could you not use a pendulum to measure mass?
Isn't a KG equal to 1 Liter of water? And that is equal to 1000 cubic cm? Length shouldn't be that hard to keep constant, and that could be narrowed down to x times the width of an atom. Why not just use that?
for example if the water is slightly different to base H2O (like if chlorine is added) the weight will be changed so weight is very difficult to measure like that
Not ... really, no. A kilogram is a measure of weight. A liter is a measure of volume. A liter of yoghurt isn't going to weigh as much as a liter of milk (or even water)
Fixing the kilogram is all well and good but what we really need is an alternative to the candela. We can't have "the luminosity of a candle" as one of the SI base units, that's just wrong.
Yes, indeed it's wrong. "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×10^12 hertz and that has a radiant intensity in that direction of 1⁄683 watt per steradian." That's how the candela is defined.
Everything in these definitions has a purpose, i learned about this in my class and the 1/683 of a watt also has a purpose (although i've forgotten it by now)
+Sam Otten All unit definitions are arbetrary, because units themselves are inherently arbitrary. It's not like it matters how we measure things. We just use what we use for historical reasons.
The watt balance relates the kilogram to electrical quantities like current and voltage. But under the current SI system, those are defined based on (among other things) the kilogram, so they'll need redefining too to avoid a circular definition.
Weights and Measures Act 1985 Schedule 1 part vi (for gb anyhow). Though in many respects the lb no longer technically exists as it's not a legal trade measure and I don't think there are physical standards left in place for imperial measures anymore
We no longer rely on a physical object to define the kilogram, but could you imagine what would happen if someone bent on causing as much chaos as possible had broken in and cut part of the international kilogram off? Based on the rule that “it always equals a kilogram, no matter what,” suddenly a kilogram is a lot smaller. It’s been hard enough trying to convince the US to use the metric system, but could you imagine telling the whole world that they now need to adopt what is effectively a new system of measurement for mass that has the exact same unit names as the old one? There would be no end to the confusion on whether things were measures in the old kilograms or the new kilograms. At that point, they’d probably have to bite the bullet and raise a second level standard kilogram to be the new official kilogram. Good thing that can’t happen anymore.
I heard that "only 1% of their userbase uses that function" or something. Because that's a good reason to make the comment section much worse for anyone actually using it for fruitful dialogue. Bollocks is what it is.
Just wanted to point out that there are plenty of physicists around the world interested in precision measurements, especially in atomic physics. It's crazy to see the precision on a second, for example, and the lengths physicists must go to to make sure the second IS as precise as they say!
When you "buy a kilogram of something in America"? We reserve metric measurements for drug dealers. Sound is measured relative to an average bald eagle's call (actually a red tailed hawk), spacial volume in eagle tears, and distance in relation to some foreign dead king's foot.
That's interesting. I remember learning in school that a kilogram was defined as the mass of a liter of water. I didn't know that had changed. The way the water thing was described to me seemed like a foolproof idea at the time. Why was it changed? Do different kinds of water have different mass, making it an inaccurate definition? Or was it something else?
it was defined with water at a specific pressure and temperature... but pressure itself is derived from mass - which meant the definition was circuitous. however, this was indeed one the historical definitions of the kilogram
I also imagine in todays world once you have a liquid kilo and you make a solid kilo there would be no real reason to use the liquid kilo afterward it would only be a less reliable weight being the inside is moving?
The weight of any object changes as it is moved from place to place. If you had a very precise scale, weighted yourself then moved to another spot, say, a mile away, you would weigh differently. This is because the earth beneath you is not homogeneous and different rocks have different densities. One of the methods for prospecting for oil along the gulf coast was to construct gravity maps. Sometimes changes in gravitational attraction can happen in as little as a few hundred feet. With this in mind, the standard weight has to be established at one point on the earth and nowhere else.
For some places that is very much correct, the California coast is exhibit A. Other places have huge areas of granite core that do not move at all. The Candian Shield for example.@@vsctutorials8355
@@vsctutorials8355 This is very much true for many places on earth, the California coast is a good example. There are some places that do not move at all. The Candian shield area is a good example. I'd think that to have a rock-solid (pun not intended) place to be made the standard for measurement, the equipment would have to be set up on an ultra-stable core place and never moved.
Doesn't the spring - or in the case of the speaker, the rubber - have an effect on the calculation of the voltage/current method? Wouldn't you have to assume the springs were all perfect and never changing?
I've put a note with my thoughts on my Facebook page - the link's in the description - but ultimately it's not predictable. No-one knows what's going to happen next!
+Tom Scott Boris Johnson knows, according to himself. Then again, Boris has become as optimistic of late as that Iraqi minister in the Second Gulf War who was declaring to the world that everything was fine while bombs were audibly dropping in the background...
What I never understood is that the kilogram was intended to represent a litre of water. But the density of (pure) water is not 1kg/litre. Not at 20degree Celcius (as most densities are usually given) and also not at 4. I can understand that better measuring methods will cause you to revise previous values. And that the water that was given 1kg/litre just wasn’t pure enough. But why now say pure water is 0,9998 instead of 1,00000 as it is intended and change the other values accordingly?
That was the definition between 1795 and 1799. Even then it was known to be such a bad definition that it was only kept in effect for four years. It's been 224 years since the kilogram had anything to do with water, and you can't just change the value now without breaking the entire world.
Veritasium and Smarter Every Day for science-y stuff, CGP Grey for very infrequent but very high-quality, well-researched videos. Numberphile, Computerphile, Sixty Symbols, Periodic Videos, and other channels done by Brady Haran for more long-form, still sciencey/mathey/computery, much more frequent videos.
I highly recommend VSauce. He explains interesting question in a really unique way. You should watch him. As for my predecessor i can second his choice on brady haran videos.
Temperature is defined in terms of absolute zero and the triple point of water. Length is defined in terms of the speed of light. Time is defined in terms of atomic hyperfine transition. Mass will soon be defined in terms of Avogadro's constant or Planck's constant.
Until we start needing to measure mass on different planets, the relationship between the two is defined by a simple constant, so unless you're talking about specific values of the weight/mass of something, it doesn't matter.
It's interchangeable in this instance. Obviously we're talking about weight, that's what we use Kilos for, but since we're establishing a set weight here it's not inaccurate to say that's it's a set mass. We're not changing gravity so the two are the same.
As the kilogram is defined as a unit of mass they are talking about a unit of mass. Weight is physically measured in Newton which is itself depending on the mass.
It's not a matter of knowing "if" they shift. Individual units will shift. Some will shift one way, some will shift in the other. The average of all remains the same. You can even have various sample groups. Perhaps three sets of 100. EDIT; Now that I'm thinking about your question. What we're talking about is really subjective vs objective, perhaps? If we all agree to call this specific measure a kilogram and that measure is drifting, the important thing is that we all agree, not the actual measure. I don't want to call what we call a kilogram arbitrary, that's why I say subjective. Can there be an objective measure of what a kilogram is and can that be a constant. Not sure. Maybe it's something we need to constantly test and maintain. I'll think on it, thanks for the video.
Thomas Vandermeiren You might get aberrant shifts in small sample sizes. It's unlikely, and less likely the more you have. That's why I suggested multiple sets. If you think of it this way. If you have two clocks and one clock runs slow, how do you know which clock is really wrong? The more clocks you have the greater accuracy. Clocks will "Shift" their measurement, but with work you're able to maintain the proper time. Though the idea of an objective measure sounds like a good idea.
***** Exactly. The idea of a kilogram is somewhat subjective. We agree on what a kilogram is and under what conditions we measure. The subjective measure is a useful tool At this point I'm wondering if there is such a thing as an objective kilogram. So this is a kilogram, but relative to what? lol
Back in the day a "lid" was the amount of "dope" it took to fill an empty Campbell's" soup can up to the line where the "red" and "white" met on the label. Critically important then....
I wish we could switch to using Planck units, rather than the metric units, which are still arbitrary. We would have to multiply each by many orders of magnitude to get them into the human scale, but then all the usual physical constants that we have to learn would just be integer powers of ten: Mass unit = 10^7 * Planck Mass ~= 0.218 kg Time unit = 10^43 * Planck Time ~= 0.539 sec Length unit = 10^35 * Planck Length ~= 1.62 meters Then, say, the gravitational constant would just be exactly 10^-12, so all we would have to remember is "-12", instead of 6.674blahblahblahx10^-11.
But then isn't the Planck system still kinda arbitrary, because we chose to calibrate it using decimal system? It would be much more practical for scientists indeed, but is it, in theory, less arbitrary than what we use today?
The funny thing is just that within the electronic world; they have a formula they use for the kilogram that is a fixed and reproducable mass. They have to do it due to needing it for their electricity equations. - But since the new kilogram mass has been redefined, their formula have had to change due to mismatching the new definition, screwing things up within the electronic world.
The redefinition of the kilogram required a correction of 0.1 parts per milion for the Volt and 0.02 ppm for the Ohm. That had an effect on calibration labs, for sure, but it went unnoticed by 99.5% of "the electronic world".
Good old International System of Units(SI) I remember studying this in university, you should make a video about that. time: second length: meter mass: kilogram electric current: Ampere temperature: Kelvin amount of substance: mole luminous intensity: candela
I thought they had already made that new definition a few years ago (with number of atoms), but apparently what I remember was just the start of that discussion...
No, they're a measurement of mass; the weight of a 1kg object is different depending on the local acceleration due to gravity, which varies by more than 1 part in 10^8 between places you'd like to make accurate measurements.
"No, they're a measurement of mass;" Part of the problem with our definition of the kilogram is that currently--while it is supposed to be a measurement of mass--is that it is inextricably tied to force (weight/gravitational pull). No matter how you slice it, the only way to actually measure "the kilogram" (the one in Paris) is by placing it on a scale and measuring the force that it and the Earth exert upon each other--which is done by seeing how far the scale is depressed (how hard "the kilogram" presses on the scale, which is to say force and not mass). The kilogram is currently based on weight, but "the kilogram's" mass and weight are one and the same because of how it is measured. So yes, the kilogram is supposed to be mass instead of weight, but unfortunately, we don't have a way to do that. When the kilogram was based on water, then it was much more easily distinguishable from weight, but that had problems that were more severe.
You could drop a box with a magnet through a horizontal magnetic field and see how different its deflection is when it contains the kilogram versus when it doesn't; that's unaffected by the local strength of gravity, so long as you calibrate it by timing how long the box spends in the magnetic field. You could also swing the kilogram around on a force gauge in a circle of a particular size with a particular period. You'll have to correct for gravity, but you can work out from the angle it swings at how much of the force you're measuring is centripetal acceleration times one kilogram. And, of course, a balance scale isn't affected by the local gravity so long as gravity is the same for both pans and there's enough gravity to keep the items in the pans. Since you're generally trying to verify that your lab's reference object has the same mass as "the kilogram", that's sufficient.
The watt balance requires more accurate resistor technology or continual adjustment: Our (The US) NIST (who holds the record for accuracy at 3.6x10^-8 relative accuracy) figured out that even resistors drift throughout the day. Still, it does seem to be the best-known method for defining a kilo.
My suggestion: We know exactly how much a liter is, correct? One liter of distilled H2O (preferably without any strange isotopes of hydrogen or oxygen)=One Kilogram. Divide by 1000. Profit.
Matthew Campbell You'd need extremely pure water, extremely stable pressure and temperature, and extremely accurate volume measurement. Too many sources of error. The methods mentioned in this video are far easier to measure with precision.
Water is simply less constant than this and i'd guess also more difficult to handle. A meter is actually defined by natural constants, and as a result a liter too.
Yes the liter is precisely defined but really if you want to make it an amount of substance, the better definition is the ball of silicon, with the number of _atoms_ made the correct definition. That could also be done for water, a certain number of water molecules to fill a liter, but it's easier I'd believe to make a precise silicon ball than a precise amount of water due to silicon being a hard and stable solid at ordinary conditions.
I already knew about the traditional kilogram and the sphere kilogram, but I watched the video anyway, and learned about the watt balance. This channel is great.
if you kept watching and didn't pause to comment, you would see he says right after "The British National Standard Kilogram"... Since he's on Britain, that's his Kilogram. The one all balances on Great Britain are measured against. He also says the International Prototype is on Paris... That's the magic of actually watching the video before commenting. You don't make yourself a fool.
Ah yes, but he did slip up in the beginning. (I actually did watch the entire video.) Let there be no confusion as to which is THE kilogram. There can only be one THE one, and that of Britain is not THE one. One musn't confuse a transfer standard for the real deal, e.g. one musn't confuse a Rubidium frequency standard for a Cesium frequency standard.
Tomatasium? The way to answer the riddle of the mass is by not trying to replicate a patron or experiment to determine it, but trying to find a way to determine it under non ideal conditions, ~ 0 G, variable temperature and pressure. Do we has the ability to associate indirectly mass with fundamental constants? In fact a lot of constants that are associated with mass will vary until there is an unify way to determine the mass.
But that watt balance thing depends on the gravitational acceleration (or how you call that in English), because what it can measure is force: the force the kilogram presses downwards on the loudspeaker, and the force you need to push the membrane back up against that other force. So it's not at all a mass measuring device.
That's was problem. All of them, from the original one in Paris, to each of the 12 copies around the world, were shifting in weight. Some gained, and some had loss. And this, despite them being kept in a tightly sealed, climate controlled rooms.
What we need is a stable, non reactive, self-isolating material. Never loses any mass, never gains any mass. Thing is, if that material was real (or common, if we're lucky, like winning the lottery every day of your life kind of lucky) we would have conquered the galaxy by now.
Note that the practicality of reproducing the kilogram from doesn't actually matter that much because physical prototype kilograms can undoubtedly be used for calibration to far better precision than the Watt Balance or any similar sort of experiment. With the pretense of ease of reproduction removed, it's obvious that the approach of fixing Avogadro's constant and defining the kilogram based on a number of some sort of atom is simpler and more physically meaningful.
a weighty issue with many opportunities for mass confusion.
thanks, dad
_shrug_ No point denying that.
this is a very massive issue, it's been weighing down on me for a long time
I like your joke a ton!
we might not understand the gravity of the situation, yet. It will be a heavy task to take on.
it depends if it's a kilogram of steel or a kilogram of feathers
but they're feathers......
Came here looking for this comment, wasn't disappointed.
But they're the same
They are the same. Even a pound of steel and a pound of feathers. But a pound of gold and a pound of feathers aren't. Well, an ounce of gold and an ounce of feathers aren't. Because an ounce of gold is a Troy ounce. (An old joke. When Troy pound existed, a pound of feathers was heavier.)
This comment is like going the wrong way down a one way street.
So apparently the new kilogram standard is this -
"The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10-34 when expressed in the unit J s, which is equal to kg m2 s -1 , where the meter and the second are defined in terms of c and ∆νCs."
Oh god that hurt my brain
And people think Fahrenheit is bad smh
This is neat. Doesn't tell us how they'll actually 𝘮𝘦𝘢𝘴𝘶𝘳𝘦 kilograms for standardisation purposes, but the definition itself is pleasingly simple and universal.
Yes, I said simple. If you don't believe me, try these two on for size:
"The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s-1."
"The candela, symbol cd, is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 x 1012 Hz, Kcd, to be 683 when expressed in the unit lm W-1, which is equal to cd sr W-1, or cd sr kg-1 m-2 s3, where the kilogram, metre and second are defined in terms of h, c and ΔνCs."
See my point? 😉
@@sakkikoyumikishi a second is the time time it takes for me to say "one thousand and one".
@@theJuggla17 Fahrenheit is defined based on kelvin, and "since 2019 the scale has been defined by fixing the Boltzmann constant k to be exactly 1.380649×10−23 J⋅K−1."
I've got a watt-balance project in the works. Still working out the details.
A channel that has 1.62M subs in 2020 had a comment with just 1 like for 4 Years!
UA-cam really is the level playing field one hopes for!
Hey Grady! Love Your videos!! One of my favourite channels out there!!
ok
Is it done?
@Practical Engineering I hope you have a plank's constant project in the works, because that's how it's defined now
And we've been still waiting!
I want a mission in GTA where you steal the kilogram and sell it back for millions.
Or steal it, chip a corner and return it. :)
In 20th of May next year the definition of a kilogram will change at it's core. Stealing that kilogram now is not such a big deal.
... as if there was no backup of that existing :D
Wow, an affidavit that that would be worth its weight in kilograms
@@krzysztofpiasek5682 warning time is near
My local drug dealer linked me to this video after ripping me off. All makes sense now. What a nice guy
It's been more than an year since the kg is based on physics laws and not an object anymore
nobody's exactly sure how much a pound is right now either
Underrated comment
Yup
Nice
Worse, they were so unsure about what a pound is, there are many kinds of pounds now.
+Alexander Tamayo Dont you get the joke?
And today 16.11.2018 The vote to change the definition of the kilogram has offically and unanimously passed in paris. SI-Units will no longer depend on physical artifacts, just on the fundamental constants of nature. Praise Science
YAY! You beat me to it!
@Nunovia Gottdamnedbizzness Noether says what?
Funny thing here, the new definition of the kilogram came into effect on the day of my physics exam, and the examinations removed a question regarding the definition, because the answer didn't hold up anymore.
11.16*
@@1brianm7 16.11, like most of the world use it
I am from the future. The kilogram is now defined based on the Planck constant, which is absolute, universal, and has units of kilogram meters-squared per second. With the physically defined meter and second, this number can be used to define a kilogram.
meters are now defined by the speed of light
i hope they will make a bigger kilogram, then I will lose weight without dieting :)
A kg is as big as you want it to be.
But it’s always one kg heavy. 🙄
@@sahibjot01 r/woooosh
@@sahibjot01 r/woooosh
@@sahibjot01 jesus christ kid calm yourself down
@@sahibjot01 Like you, kiddo
1kg = 1000g duh
But you kep going down and down.
+Ninja lemur he's joking
Dilip Tien oh noes, you found out!!!
1g = 1000mg duh
the best cameraman kilogram/1000
That sphere reminds me of vertasium's world's roundest object video....
Because it was a similar item meant for the same purpose.
I actually thought it was the same sphere from veritasium's video
Niall Kinsella
Maybe it is?
tf guys, that's the similar sphere from veritasium video
awesome video, I've watched it soo many times, It's fascinating and ingenious to see the Metric system was invented in all of its glory!!
1:46 how did they get that photo without a camera in the reflection pointing it?
is that block in the middle not Tom’s phone on a stand?
@@marielikes2502 what ever that is (phone or otherwise) it's definitely what took the video.
It's a video, not a photo.
@@marielikes2502 yes, but the reason why MrLagEveryP2WServer was confused was because it looks like the guy in the background is doing things on top of it.
"Operation Gram Slam, Mr. Bond is where my team of svelt cat burglars shave milligrams off *the* Kilogram thus increasing the amount of all my stuff. Ha ha!"
"But wouldn't that increase everyone's stuff equally, Gramfinger?"
"oh .. yeah."
I'm surprised we don't all use a unit of mass based on 1 MOL of pure water at its exact freezing point, or something else more definitive.
There was an attempt to standardize kilogram as a liter of water at 0°C and under atmospheric pressure, but the problem as, that pressure units are derived from are and mass, so it would refer to itself.
The mass of 1mol of water would not change based on temperature
The silicone sphere is the same thing, 100% definitive and easier to handle than water...
Isn't the definition of a kilogramme 1L of pure H2O at 4°C?
Kenji Gunawan no
Nobody exactly sure how much a kilogram is right now... Specially Americans
Yupie. What's a km? Kanadian miles?
~2 lbs
🦅🇺🇸🦅🇺🇸🦅🇺🇸🦅🇺🇸🦅🇺🇸🦅🇺🇸🦅🇺🇸🦅🇺🇸🦅🇺🇸
This is *SATIRE*
I am american, and am constitutionally allowed to make this joke.
@@Attaxalotl Not if you're from Puerto Rico, Guam, Samoa or others :(
I worked for the Metrology Lab at NMSU it was pretty cool. It was kind of weird because we got a lot of shipments from all over New Mexico to validate their weight… it's kind of weird when it's like, “Package weight: 1 kg ± 5 µg”
Apparently, there's a set of weights that keeps getting posted around to the various state metrology labs and they weigh them and compare results. It was kind of cool. :)
I briefly worked at the International Bureau of Weights and Measurements, at the masses department, I could have a glance at the Kibble scale, that machine made to correlate the kilogram to the Planck constant so we don't rely on standard masses anymore. That thing is so precise it can catch the gravitational gradient across the room. Heck it even has to take into account its own gravitational field in the computation. They put it in in a basement room after removing the floor, so it has no physical contact with the building.
Well explained tom. I find metrology is a subject people either click with instantly or just seem puzzled by the whole thing all together. Good concise explanations of some quite complicated information. NPL have excellent training information too so good to see they have a channel, thanks
Man! So cool all the random stuff you do videos on. I also like when you get guests to chip in on their fields of expertise.
0:01 "You may be a doctor, but I am THE Doctor. The definite article, you might say."
That line hit hard at the end of The Doctor Falls
I only just found toms channel a few days ago, I can't stop watching it. He's so entertaining in a nerdy way
The watt balance thing is amazing! That is definitely the most practical way of doing it, though there is more room for error in execution that won't result in an obvious failure.
Surely the main problem with it is that gravity isn't constant around the world, whereas the kilogram is a unit of mass and needs to be independent of such things?
Exactly, using weight to mesure mass is problematic.
+d2factotum yeah good point. And what about the equipment you use to measure it?
For the majority of the world gravity is considered to be constant as the relative height differences between different counties compared to the radius of the earth is most of the time insignificant. But for the absolute 1 kg mass it would make a difference. So how about using the watt balance at agreed radius from the centre of the earth so that gravity would be constant and the weight of a 1 kg mass would also be the same.
Wilron
Gravity isn't constant even at constant radius from the centre of the Earth--local geology can make a difference. Not a large difference, but when you want something to be accurate to better than a millionth of a percent, an important difference. Also, how would you accurately measure your distance from the centre of the Earth in the first place?
Is that the same sphere that Veritasium touched? =)
Newest comment
No. The sphere that Veritasium touched was the "most spherical object" in the world which is different to this one
wtf youtube comment posted 6 minutes ago reply 9 minutes ago
Which is the same thing if not the exact same sphere.
did you jsut see the title of the video and not watch it? the whole point of the spehere was a base kilogram unit
"Quit polishing your kilogram!"..."I'm polishing my kilogram right now baybeee!"
Just wanted you to know You're one of the reasons I switched my major to computer science. It's a joy watching you! Cheers from Texas!
Oh, please get a job with Texas Instruments and make me an overpowered calculator.
Thank god, it's been forever since Veritasium talked about this, I've been waiting for an update
+Tom Scott, you should do a video at the The National Museum of Computing at Bletchley Park.
Just when I thought I was fully geeked out, I turned around and saw the slide rules....
I love learning about stuff like this, we never really think about where we get our measurements from.
This is actually strangely relevant to me right now, as I'm doing some worldbuilding, and trying to figure out some mathematical constants for my universe.
Having been to the NPL I can confirm its an amazing place, they have the darkest room in Europe there, as well as an insanely cool anechoic chamber.
As an aside, could you not use a pendulum to measure mass?
How would you use a pendulum to measure mass? (Seems like there's some way that I'm not aware of, so I'm genuinely curious)
I love the randomness of the topics you cover. always something interesting!
Isn't a KG equal to 1 Liter of water? And that is equal to 1000 cubic cm?
Length shouldn't be that hard to keep constant, and that could be narrowed down to x times the width of an atom. Why not just use that?
+Gavers23 Not quite! And that depends on a lot of qualities of the water…
for example if the water is slightly different to base H2O (like if chlorine is added) the weight will be changed so weight is very difficult to measure like that
+Tom Scott are you going to talk about brexit?
Wait, are you an Arandanaut?
Not ... really, no. A kilogram is a measure of weight. A liter is a measure of volume. A liter of yoghurt isn't going to weigh as much as a liter of milk (or even water)
wow that sphere looks heavy, i wonder how much it weighs
Fixing the kilogram is all well and good but what we really need is an alternative to the candela. We can't have "the luminosity of a candle" as one of the SI base units, that's just wrong.
Yes, indeed it's wrong.
"The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×10^12 hertz and that has a radiant intensity in that direction of 1⁄683 watt per steradian."
That's how the candela is defined.
luxs?
That's still just disgustingly arbitrary. 1 watt per steradian would at least be seemingly logical.
Everything in these definitions has a purpose, i learned about this in my class and the 1/683 of a watt also has a purpose (although i've forgotten it by now)
+Sam Otten All unit definitions are arbetrary, because units themselves are inherently arbitrary. It's not like it matters how we measure things. We just use what we use for historical reasons.
The watt balance relates the kilogram to electrical quantities like current and voltage. But under the current SI system, those are defined based on (among other things) the kilogram, so they'll need redefining too to avoid a circular definition.
Well, looks like it is time to go back to English units, we will just take an average of everyone's foot size and go with that.
And then gravity changes just to f*** you over.
It wouldn't matter, that is the constant, we'd still use that as our Kilogram.
They're measuring mass, not weight. You should see how volts are defined, you need an infinitely long pair of conductors.
Weights and Measures Act 1985 Schedule 1 part vi (for gb anyhow). Though in many respects the lb no longer technically exists as it's not a legal trade measure and I don't think there are physical standards left in place for imperial measures anymore
its probably less now, considering we "left" the eu
A Banana hence the "left"
watt*
but the left didn't want to leave... xD
now y'all did leave the eu
beanard In theory ...
We no longer rely on a physical object to define the kilogram, but could you imagine what would happen if someone bent on causing as much chaos as possible had broken in and cut part of the international kilogram off? Based on the rule that “it always equals a kilogram, no matter what,” suddenly a kilogram is a lot smaller. It’s been hard enough trying to convince the US to use the metric system, but could you imagine telling the whole world that they now need to adopt what is effectively a new system of measurement for mass that has the exact same unit names as the old one? There would be no end to the confusion on whether things were measures in the old kilograms or the new kilograms. At that point, they’d probably have to bite the bullet and raise a second level standard kilogram to be the new official kilogram.
Good thing that can’t happen anymore.
I needed a laugh
How about doing a video about why UA-cam no longer cites the person you're replying to in the comment section?
look at that bullshit! they removed all the spaced lines. the bastards!
It does
+Minecraftster148790 like this
I heard that "only 1% of their userbase uses that function" or something. Because that's a good reason to make the comment section much worse for anyone actually using it for fruitful dialogue. Bollocks is what it is.
Cyril Nope. I've tried. But it still works when you reply using the "bell" notifications.
Just wanted to point out that there are plenty of physicists around the world interested in precision measurements, especially in atomic physics. It's crazy to see the precision on a second, for example, and the lengths physicists must go to to make sure the second IS as precise as they say!
When you "buy a kilogram of something in America"? We reserve metric measurements for drug dealers. Sound is measured relative to an average bald eagle's call (actually a red tailed hawk), spacial volume in eagle tears, and distance in relation to some foreign dead king's foot.
he's just optimistic about the future
It's fantastic that i can't tell how much of this comment is satire
Also isn't velocity American Flags'waves per bullet?
Tom! Next year, on Mid-summer's Solstace; go to Alesund and experience Slinningsbålet!!
That's interesting. I remember learning in school that a kilogram was defined as the mass of a liter of water. I didn't know that had changed. The way the water thing was described to me seemed like a foolproof idea at the time. Why was it changed? Do different kinds of water have different mass, making it an inaccurate definition? Or was it something else?
it was defined with water at a specific pressure and temperature... but pressure itself is derived from mass - which meant the definition was circuitous. however, this was indeed one the historical definitions of the kilogram
I also imagine in todays world once you have a liquid kilo and you make a solid kilo there would be no real reason to use the liquid kilo afterward it would only be a less reliable weight being the inside is moving?
Or we could just go back to using Imperial everywhere and worrying about the length of a barleycorn.
the original definition of a kilogram was 1 litre of water
so why don't we just put a litre of water in a jug and call it a day?
LARAUJO How do you know the markings on the measuring device are accurate and haven't changed since then?
Volume depends on temperature so a liter of water wouldn't weigh the same at all temperatures.
And assuming water doesn't compress or expand much due to the change in the atmospheric pressure
Water is simply less constant than this and i'd guess also more difficult to handle.
why not just say a gram is 1 cubic centimeter of some metal
The weight of any object changes as it is moved from place to place. If you had a very precise scale, weighted yourself then moved to another spot, say, a mile away, you would weigh differently. This is because the earth beneath you is not homogeneous and different rocks have different densities. One of the methods for prospecting for oil along the gulf coast was to construct gravity maps. Sometimes changes in gravitational attraction can happen in as little as a few hundred feet. With this in mind, the standard weight has to be established at one point on the earth and nowhere else.
Rocks move under this one spot
For some places that is very much correct, the California coast is exhibit A. Other places have huge areas of granite core that do not move at all. The Candian Shield for example.@@vsctutorials8355
@@vsctutorials8355 This is very much true for many places on earth, the California coast is a good example. There are some places that do not move at all. The Candian shield area is a good example. I'd think that to have a rock-solid (pun not intended) place to be made the standard for measurement, the equipment would have to be set up on an ultra-stable core place and never moved.
"a pint's a pound the world around" - sorted [sheesh]
Doesn't the spring - or in the case of the speaker, the rubber - have an effect on the calculation of the voltage/current method? Wouldn't you have to assume the springs were all perfect and never changing?
And I always thought the definition of a kilogram was the mass of exactly 1 liter of water at standard temperature and pressure. Seems I was wrong.
This was the definition between 1795 and 1799. You are slightly out of date.
"...fairly easy to produce."
oh neat so maybe I could like buy one for decoration then-
"costs 2.5 million euros."
*oh*
Tom, will you give your impression at some point about Brexit ?
I've put a note with my thoughts on my Facebook page - the link's in the description - but ultimately it's not predictable. No-one knows what's going to happen next!
+Tom Scott Boris Johnson knows, according to himself. Then again, Boris has become as optimistic of late as that Iraqi minister in the Second Gulf War who was declaring to the world that everything was fine while bombs were audibly dropping in the background...
What I never understood is that the kilogram was intended to represent a litre of water. But the density of (pure) water is not 1kg/litre. Not at 20degree Celcius (as most densities are usually given) and also not at 4. I can understand that better measuring methods will cause you to revise previous values. And that the water that was given 1kg/litre just wasn’t pure enough. But why now say pure water is 0,9998 instead of 1,00000 as it is intended and change the other values accordingly?
That was the definition between 1795 and 1799. Even then it was known to be such a bad definition that it was only kept in effect for four years. It's been 224 years since the kilogram had anything to do with water, and you can't just change the value now without breaking the entire world.
Anyone got any channel recommendations that are as high quality as this channel?
I find "sharkee" pretty good, and he doesn't have many subscribers.
+Simon Clarkstone Really?! 72000 is quite a lot of people
Veritasium and Smarter Every Day for science-y stuff, CGP Grey for very infrequent but very high-quality, well-researched videos. Numberphile, Computerphile, Sixty Symbols, Periodic Videos, and other channels done by Brady Haran for more long-form, still sciencey/mathey/computery, much more frequent videos.
I highly recommend VSauce. He explains interesting question in a really unique way. You should watch him. As for my predecessor i can second his choice on brady haran videos.
I'd suggest Nerdwriter1. He just brilliant!
Temperature is defined in terms of absolute zero and the triple point of water.
Length is defined in terms of the speed of light.
Time is defined in terms of atomic hyperfine transition.
Mass will soon be defined in terms of Avogadro's constant or Planck's constant.
Sooo... are we talking about weight or mass? You mentioned both.
Until we start needing to measure mass on different planets, the relationship between the two is defined by a simple constant, so unless you're talking about specific values of the weight/mass of something, it doesn't matter.
Titanium1500 This is physics goddammit. Our measurements should work perfectly even on the edge of a black hole! :)
It's interchangeable in this instance. Obviously we're talking about weight, that's what we use Kilos for, but since we're establishing a set weight here it's not inaccurate to say that's it's a set mass. We're not changing gravity so the two are the same.
As the kilogram is defined as a unit of mass they are talking about a unit of mass. Weight is physically measured in Newton which is itself depending on the mass.
+Fabian Neundorf yes, because if this object has a MASS of 1Kg, the its weight is actually 9.8N on earth.
Another great video Tom keep up the good work
1:05 Me with broken earbuds: it doesn't matter is it's GAY (silence) amount of mass-
Tom , that plan/drawing on the wall to the right of where you are standing at the beginning . can we have a closer look at that ... it looked cool
Why not just keep a 100 of them. When you want to know how much a kilogram is measure them all, the average is the kilogram.
+MrDeadInMyPocket That's basically what they do (there are many copies) - but how would you know if they all shifted in sync?
It's not a matter of knowing "if" they shift. Individual units will shift. Some will shift one way, some will shift in the other. The average of all remains the same. You can even have various sample groups. Perhaps three sets of 100.
EDIT; Now that I'm thinking about your question. What we're talking about is really subjective vs objective, perhaps? If we all agree to call this specific measure a kilogram and that measure is drifting, the important thing is that we all agree, not the actual measure. I don't want to call what we call a kilogram arbitrary, that's why I say subjective. Can there be an objective measure of what a kilogram is and can that be a constant. Not sure. Maybe it's something we need to constantly test and maintain. I'll think on it, thanks for the video.
That's why Tom mentioned the "in sync" bit... If they all shift to the same side of the scale, you'd have no way of knowing.
Thomas Vandermeiren
You might get aberrant shifts in small sample sizes. It's unlikely, and less likely the more you have. That's why I suggested multiple sets.
If you think of it this way. If you have two clocks and one clock runs slow, how do you know which clock is really wrong? The more clocks you have the greater accuracy. Clocks will "Shift" their measurement, but with work you're able to maintain the proper time.
Though the idea of an objective measure sounds like a good idea.
*****
Exactly. The idea of a kilogram is somewhat subjective. We agree on what a kilogram is and under what conditions we measure.
The subjective measure is a useful tool At this point I'm wondering if there is such a thing as an objective kilogram. So this is a kilogram, but relative to what? lol
When this absolute method of measuring/defining a kilogram is fully developed, I'd love a follow-up video, please!
Or we just go back to a liter of water.
Pan kurczak But at least it's stays consistant in the long term. Every once in a while you do a refresh.
Yeah because the mass of a litre of water is constant right
But the mass of the water will still depend on temperature and ambient pressure
Actually it is supposed to be at 4 degrees celsius
Yep, the temperature is given as 4 degrees celsius, when water is at its densest.
Back in the day a "lid" was the amount of "dope" it took to fill an empty Campbell's" soup can up to the line where the "red" and "white" met on the label. Critically important then....
Expected something about Brexit!
It's quite refreshing that it wasn't
+Zack Miller Don't worry, it's not weighing down by much. It's in pounds remember.
+Zack Miller *a very limp 'ba dum tss'*
+BOSK *a slightly less limp 'ba dum tss'*
Why can't I see the camera's reflection in shots like 2:11? Am I just missing it?
I wonder if the british standard kilogram can drop as hard as the british pound.
Dark
This is one of the few facts you've shared I actually knew!
Hey tom, will brexit affect your videos? thanks
Hi IUNFE,
No it really won't,
I like your name.
Hodor:D
he made one when he entered Russia without Visa
once he's no longer EU citizen, stuff like this will be harder
+666Tomato666 it'll still be possible.
I wish we could switch to using Planck units, rather than the metric units, which are still arbitrary. We would have to multiply each by many orders of magnitude to get them into the human scale, but then all the usual physical constants that we have to learn would just be integer powers of ten:
Mass unit = 10^7 * Planck Mass ~= 0.218 kg
Time unit = 10^43 * Planck Time ~= 0.539 sec
Length unit = 10^35 * Planck Length ~= 1.62 meters
Then, say, the gravitational constant would just be exactly 10^-12, so all we would have to remember is "-12", instead of 6.674blahblahblahx10^-11.
It's actually surprisingly large: ~21.8 micrograms. Not all Planck units are incredibly tiny.
But then isn't the Planck system still kinda arbitrary,
because we chose to calibrate it using decimal system?
It would be much more practical for scientists indeed, but is it, in theory, less arbitrary than what we use today?
hoped i was the thousand viewer so i could be the kiloviewer :D
This doesnt make really sense bc kgs can be translated to 1kg = 1000000mg also 1kg = 10hg or 1kg = 100dag
moomin renjun Kilo means thousand.
2:34 but is it the same if a different speaker is used?
no it doesn't weigh 1Kg, it weighs 9.8N.
But what if he's filming this on the moon
b 28282 then it would be 1.6N I think
Nothing weights Newton. Newton is a Force, that's why it can vary
Daniel Palaci weight is the force downwards due to gravity, weight is a force. Kg is for mass. W=mg.
Yea you are right. I got confused with mass.
The funny thing is just that within the electronic world; they have a formula they use for the kilogram that is a fixed and reproducable mass. They have to do it due to needing it for their electricity equations. - But since the new kilogram mass has been redefined, their formula have had to change due to mismatching the new definition, screwing things up within the electronic world.
The redefinition of the kilogram required a correction of 0.1 parts per milion for the Volt and 0.02 ppm for the Ohm.
That had an effect on calibration labs, for sure, but it went unnoticed by 99.5% of "the electronic world".
Finally we can say that a Kilogram of steel is heavier than a Kilogram of feathers.
Because steel is heavier than feathers.
But they're both a kaelogram....
@@wisdry But they're both a kaelogram
but steel is heavier than feathers
but can it run crysis
Good old International System of Units(SI) I remember studying this in university, you should make a video about that.
time: second
length: meter
mass: kilogram
electric current: Ampere
temperature: Kelvin
amount of substance: mole
luminous intensity: candela
Veritasium already made a good video about this.
it was about curvature not weight
+SCOFIE he did one about weight as well.
Exactly what I was thinking
it was the same object, it needs to be perfectly spherical in order to measure it accurately
+Pan kurczak
Watch the video again. Dirk explained that the kilogram sphere is the most spherical thing.
I thought they had already made that new definition a few years ago (with number of atoms), but apparently what I remember was just the start of that discussion...
But kilograms aren't weight...
Not by their strictest definitions, but as far as standardized units of measure are concerned, they are interchangeable.
They are a measurement of weight
No, they're a measurement of mass; the weight of a 1kg object is different depending on the local acceleration due to gravity, which varies by more than 1 part in 10^8 between places you'd like to make accurate measurements.
"No, they're a measurement of mass;"
Part of the problem with our definition of the kilogram is that currently--while it is supposed to be a measurement of mass--is that it is inextricably tied to force (weight/gravitational pull).
No matter how you slice it, the only way to actually measure "the kilogram" (the one in Paris) is by placing it on a scale and measuring the force that it and the Earth exert upon each other--which is done by seeing how far the scale is depressed (how hard "the kilogram" presses on the scale, which is to say force and not mass). The kilogram is currently based on weight, but "the kilogram's" mass and weight are one and the same because of how it is measured.
So yes, the kilogram is supposed to be mass instead of weight, but unfortunately, we don't have a way to do that. When the kilogram was based on water, then it was much more easily distinguishable from weight, but that had problems that were more severe.
You could drop a box with a magnet through a horizontal magnetic field and see how different its deflection is when it contains the kilogram versus when it doesn't; that's unaffected by the local strength of gravity, so long as you calibrate it by timing how long the box spends in the magnetic field.
You could also swing the kilogram around on a force gauge in a circle of a particular size with a particular period. You'll have to correct for
gravity, but you can work out from the angle it swings at how much of
the force you're measuring is centripetal acceleration times one
kilogram.
And, of course, a balance scale isn't affected by the local gravity so long as gravity is the same for both pans and there's enough gravity to keep the items in the pans. Since you're generally trying to verify that your lab's reference object has the same mass as "the kilogram", that's sufficient.
The watt balance requires more accurate resistor technology or continual adjustment: Our (The US) NIST (who holds the record for accuracy at 3.6x10^-8 relative accuracy) figured out that even resistors drift throughout the day. Still, it does seem to be the best-known method for defining a kilo.
My suggestion:
We know exactly how much a liter is, correct? One liter of distilled H2O (preferably without any strange isotopes of hydrogen or oxygen)=One Kilogram. Divide by 1000. Profit.
Matthew Campbell You'd need extremely pure water, extremely stable pressure and temperature, and extremely accurate volume measurement. Too many sources of error. The methods mentioned in this video are far easier to measure with precision.
How do you know that's one liter of water just as you don't know what's a kilogram of water
Water is simply less constant than this and i'd guess also more difficult to handle.
A meter is actually defined by natural constants, and as a result a liter too.
Yes the liter is precisely defined but really if you want to make it an amount of substance, the better definition is the ball of silicon, with the number of _atoms_ made the correct definition. That could also be done for water, a certain number of water molecules to fill a liter, but it's easier I'd believe to make a precise silicon ball than a precise amount of water due to silicon being a hard and stable solid at ordinary conditions.
I already knew about the traditional kilogram and the sphere kilogram, but I watched the video anyway, and learned about the watt balance. This channel is great.
The watt balance is a very interesting concept.
That's not THE kilogram, THE kilogram is the one in Paris.
if you kept watching and didn't pause to comment, you would see he says right after "The British National Standard Kilogram"...
Since he's on Britain, that's his Kilogram. The one all balances on Great Britain are measured against.
He also says the International Prototype is on Paris...
That's the magic of actually watching the video before commenting. You don't make yourself a fool.
Yes, he made a major point of saying this in the video.
ha! loser responding to a comment
Ah yes, but he did slip up in the beginning. (I actually did watch the entire video.) Let there be no confusion as to which is THE kilogram. There can only be one THE one, and that of Britain is not THE one. One musn't confuse a transfer standard for the real deal, e.g. one musn't confuse a Rubidium frequency standard for a Cesium frequency standard.
Just admit you didn't watch the full video and wanted some "AKCHUALLY" points
Tomatasium? The way to answer the riddle of the mass is by not trying to replicate a patron or experiment to determine it, but trying to find a way to determine it under non ideal conditions, ~ 0 G, variable temperature and pressure. Do we has the ability to associate indirectly mass with fundamental constants? In fact a lot of constants that are associated with mass will vary until there is an unify way to determine the mass.
silly Brits and your metric system
everybody knows that 12 oz= 1 pound= 3 feet = 1 yard
And it's interchangeable across units! Divide that by a hogshead and you get the furlong! Brilliant!
Actually the metric system was invented by the french.
1 pound equals 3 feet. God bless America. Also, 16 ounces in a pound m88!
It's not 'our' metric system any more than Fahrenheit is 'our' system.
Actually the current imperial measurement system is now based on the metric system because it's much more stable. Sad but true.
A €2.5mm perfect kilogram sphere would be a dope desktop trinket.
But that watt balance thing depends on the gravitational acceleration (or how you call that in English), because what it can measure is force: the force the kilogram presses downwards on the loudspeaker, and the force you need to push the membrane back up against that other force. So it's not at all a mass measuring device.
Ralesk they simultaneously measure local gravity using a gravimeter. Then the forces cancel, leaving mass alone.
I went past the NPL last Thursday. Thought it sounded cool and I'd like to go there.
0:14 "weighs"?
That face that Tom pulls at the end of his last statement in each video...
Check out the Veritasium video on the silicon sphere as well, it's good.
1:30 Just tune a weight to the kilogram, and measure it's mass several months later to see if it has changed.
That's was problem. All of them, from the original one in Paris, to each of the 12 copies around the world, were shifting in weight. Some gained, and some had loss. And this, despite them being kept in a tightly sealed, climate controlled rooms.
What we need is a stable, non reactive, self-isolating material. Never loses any mass, never gains any mass. Thing is, if that material was real (or common, if we're lucky, like winning the lottery every day of your life kind of lucky) we would have conquered the galaxy by now.
@@Adahn99 Stable and non-reactive... Damn, I wish there are noble gases with a lower atomic number than radon!
There should be a law that calling that thing a "lump" should be a criminal offense
you should also explain how the other 'definition' of 1 litre of water = 1Kg is not workable either
Veritasium did a great video on this topic. The CSIRO have taken great steps already.
You should update this video Tom. Now we only use math to find the kg value from Planck's constant
Note that the practicality of reproducing the kilogram from doesn't actually matter that much because physical prototype kilograms can undoubtedly be used for calibration to far better precision than the Watt Balance or any similar sort of experiment. With the pretense of ease of reproduction removed, it's obvious that the approach of fixing Avogadro's constant and defining the kilogram based on a number of some sort of atom is simpler and more physically meaningful.
I remember when Veritasium did a video about this. I'm guessing this is more of an update to that by another channel.