I appreciated the giggle at the end. The guy basically said "solve this simple algebra equation and redefine the two fundamental units of ALL OF PHYSICS".
I'm pretty sure I had this guy for high school physics 8:23 - mumble mutter something-or-other (very fast and in a difficult to understand accent), "simple -don't you see, dummkoff?" 🤔
+SmarterEveryDay yeah, I thought that was fascinating- not only did they have to map it, they then had to calculate what it would be at the center of mass including the influence of the balance itself
Hey Veritasium I was part of the team working with Bryan Kibble on the NPL mkII Kibble Balance (aka Watt Balance, aka Moving Coil experiment) between 1991 and 2000. Firstly I'd like to congratulate you on a great video. It's not easy explaining this elegant but complex method of redefining the kg and you guys did a good job. One thing to possibly add is the importance of keeping the magnetic field constant. Both weighing and velocity measurements are not quick and are conducted over a long time period. Back then it lasted over an hour, and the field strength is highly susceptible to temperature changes, so keeping the large magnet at a constant temperature is imperative. I worked on the NPL system and we managed to keep the temperature drift down to a millikelvin or two over the duration of measurement, usually overnight.
If I understand your question correctly, I think you are mistaken. The "g" in the equation is g as in "Gravitational acceleration", not g as in "gram". It's measured in m/s^2. The video at 7:31 explains how they determine the local value of g with very high accuracy.
Hello Robin, My mind boggles at how we've improved accuracy from measuring in sticks, stones and body parts to tiny fractions of fundamental constants. Also, I find it poetic that we use equipment that needs a crane to lift and assemble to perform measurements so sensitive, that would be affected by the operator's kids changing the TV channel at home.
@@idjles you measure the free-fall acceleration due to gravity. they do that by dropping a reflecting cube down an evacuated pipe and using a laser to measure the acceleration.
Parrot-hD Actually those cylinders will probably still be used. They won't be used as a definition anymore, but as a pattern. You can't have a Watt Balance on every laboratory, what they do is send their instruments to a place where these will be calibrated, and for the calibration they will probably still use the cylinders because of sheer convenience.
Gabriel, actually they will most likely make new weights instead of changing the ones they already have. the mass in France will probably end up in a museum
But they'll be remembered as they should be: in a museum, for the value they contributed to humanity. The prototype kilograms helped put people into space, make metal ships that can float in our oceans, helped us determine Planck's Constant. They have been immensely useful. We're graduating to something better, moving on as a species. Aren't all of these good things?
University nowadays = all about degree certificates. Genuinely skilled graduates are those who invested countless hours teaching themselves cause Uni courses are typically not great in imparting knowledge that lasts long in the brain.
... You should really know most of this stuff. Maybe not Josephson Junctions or Quantum Hall but hopefully you would have seen those in a Lab. Everything else is first year stuff though? If that.
@@elendilion : That's right. A team of scientists from the National Institute of Standards & Technology went to a local Home Depot and took a random Planck of wood off the shelf and measured the weight, divided that weight by Planck's constant, and that became the basis of the new kilogram.
I will not lie, and tell you that I understood everything that you just said, but enough to understand that an amazing amount of work happens behind the scenes to provide the folks like me that use these standards daily to be able to rely on them being constant. I enjoy your channel.
I'm doing my semestral project on this topic and I have to admit it's really crazy! That amount of work they put into this is just astonishing. Everything has to be perfect, everything has to be measured precisely many times and when they are done, they improve the Watt balance and have to start all over again.
Well, unless you're a physicist you probably don't rely on this, considering that all of the measuring equipment that anyone uses is going to be off by magnitudes more than those 'innacurate' standard weights they spoke of at the start
The U.S. has its own gallon (3.78 litres, vs 4.54 litres), which is different than the imperial gallon used in most other countries (that don't use metric or use both).
Why would you want to discard the superior imperial system in favor of this overly complex SI-nonsense? Being able to measure mass, weight and money using the same unit is convenient.
the kilogram is now the energy of a gamma-ray photon which does not exist, which cannot be produced, and which is completely 100% fictional and has a wavelength which is approximately a million times smaller than the width of a quark. What does that say about the level of scientific development...? Not something science should be proud of.
@@eggue9598 the kilogram's redefinition equates the mass of 1kg to the energy of a gamma ray which is so energetic that has a wave length a million times smaller than the smallest matter particle present day physics has concieved - the quark. this gamma ray photon is so energetic that radiation of photons with that same frequency can never be produced on Earth. it is a fictional photon, that humans cannot experiemce, produce, interact with, etc.
@Eggue, but it does mean that it doesn't exist for humans because humans cannot produce it (too much energy - 20 Mtons of TNT equivalent per photon) or measure it (no equipment to measure such radiation), and if humans were unlucky enough that the planet gets exposed to radiation of such photons passing by, each photon from that radiation will deliver a blow over 1000 times larger than Heroshima.
Kai Widman Not only, but also in the US. See the overview at 8:20 for some of the others. I can't identify all, but at least France (LNE), Japan (NMIJ), and Germany (PTB) are involved. This is for the balance only, others must be added for Avogadro counting. It's a worldwide cooperative effort, by about everyone having enough money to participate.
I couldn't stop smiling through this whole thing. My face hurts. As an amateur Electrical, Mechanical, and Structural Engineer. Just seeing what it takes to maintain the consistency of measurements, is really interesting & exciting to me. Thank you, this channel, for showing me this. And I thank the scientists doing that.
My physics teacher literally recommended your channel to our class, guess who's watching your videos now? Edit: As a VWO6 student I should know how to speak English XD, dutch people will understand
The Quantum Hall effect is crazy complicated. You need grad physics background to really understand even it's simplest integer form. More complicated fractional forms are still being researched to this day. Really cool though. I hope Derek is up to the challenge.
I am quite happy i don´t have to learn this definition in physics class and could stick with the old definition. So this new definition alone could be enough for a single exam.
I always knew that the Kilogram would be made into a true constant similarly to how the meter and other units of measure have been. This solution is just so elegant in its simplicity (despite not being simple to carry out) that I find it beautiful.
TheSoulStealingGinger it's civil research. that kind of research doesn't know boarders for decades. you probably have dozens of scientists of different nationalities work on that. also that scientist has a very strong Austrian German accent ;)
The effort with the Silicon thing is a world wide effort. The raw silicon was created in Germany, than send to Russia for refinement, than send back to Germany to form a monocrystalline structure, than spheres were formed in different country, one of them Australia and measurements also take place around the world.
TheSoulStealingGinger I remember hearing from somewhere that the US govt. officially recognizes the metric system, but does not officially recognize the imperial system. In fact, all modern definitions of imperial measurements are defined by metric counterparts (the inch is defined as 2.54 cm for example). Measurements for science and engineering are always in metric. However, too much of the US's populace is too used to imperial, so changing all the signs and books in the country would be both be expensive and not very fruitful.
Even though I have only taken a basic level high school physics course, I still really enjoyed the use of the equations to illustrate the complicated nature of this problem. I tried to follow along, and I'm sure I failed, but I got the gist of it.
I mean, having taken all of the high-school physics lessons and having touched on college physics too, I can certainly tell that those formulas were quite simple for something as huge and important. Still not SO simple, and also they're used with high-tech measurements, so not at the reach of any physicist, but it's really cool that something as important is also so understandable.
Kai Widman Everything he did with the math is basic Algebra. No physics knowledge is needed to see what is happening. If you want to know more about why these particular formulas work, you need knowledge of physics.
Here is a question: Why is the unit of weight for solids is 1 kilogram and for liquids 1 liter? Should it not be 1 gram or 1 kiloliter? I mean 1 kg is already 1000g. Also 1 kg water = 1 liter kind of odd. It should be gram and 1 liter so then 1g=1l simple.
The liter is a unit of volume, not mass, which the kg is. The world "weight" is sometimes used for the downward force of an object, and sometimes for its mass. Besides, the volume of 1 kg of water is dependent on its temperature, to be precise. Re your final comment, the gram was defined when a different system of units was being used - CGS for centimeter, gram, second, and when the switch to MKS (meter, kilogram, second) was made it tied everything together.
sonicspring l know about weight and liquid. I was talking about different powers of 10 for similar units of measure. Thanks for the reply. I was hopin youtube gods would answer. I thought it was a worthy question.
A teacher once explained it to me. Here's what I remember! Back when the first metric system was being proposed the standard for mass was named 'Grare' (I don't know what it means, I don't speak French). The French Revolution was also happening at the same time and, apparently, 'Grare' also was a reference to the nobility, so for the sake of not being beheaded they changed it to gram, and they reduced its size to help bakers and stuff make small measurements (like the amount of flour they needed to make bread) more consistent. Later they realized that most people were not measuring small enough masses for the gram to be convenient, and since they couldn't go back to the 'Grare' they just multiplied the gram by a thousand and left it at that. After the French Revolution, most of the world just accepted the kilogram as a standard and asked no questions because it was convenient, I guess. Again, I may be forgetting a lot of details since I don't speak French and I heard the story ages ago, but that was the gist of it
anderson Smith I recommend looking up the "roundest object in the world" video, also by Veritasium. He not only explains the other method of fixing the kilogram (a sphere of silicon atom), he also explains how the kilogram got its name.
The SI unit of mass was actually the gram. But it was too small for practical use and so the Kilogram was made into the SI unit of mass. Renaming the kilogram and shifting everything down by 10^3 would just cause confusion.
it would be cool if we measured a kilogram by how much light bends when it passes by 1KG due to the gravitational dip in the fabric of space time.. impossible but quantifiable
That actually sounds great but i think that it would require a measurement system so sensible that i don’t know if it exists, a perfect sphere, and I'm not sure if you can do the measurements on the surface of the earth.
As a kid who grew up with public education and working parents I just wish videos like this would have been around when I was a kid. Not that I have any complaints because I don't but I can only imagine that my life would have probably taken a much different path. Physics is such a fascinating subject.
Nihilore - Royalty Free Music Was going to say this too. I'm really enjoying watching Derek's videos and seeing his meta-experiment in action. I hope he shares if this much more technical video fares differently in RU-vid's algorithms than the other, more simple ones he's been experimenting with lately.
That's always a thought I had. What if these constants weren't fixed? Maybe, in some other part of the universe they change? It's all very sci-fi buts it's interesting to ponder :D
Exactly what I was thinking. or what if they change in time and 10,000 years from now they won't understand how adult humans weighed 100 kg because it could have shifted an order of magnitude lower. The science does seem pretty clear right now that these are constant. But how will we know later if this changes? Also, it might be a stretch, but is it possible to measure these to such precision relative to each other? Does quantum uncertainty itself not affect our ability to measure these constants to such a degree of precision? I would imagine they considered that for this application though... But quantum theory has only been around 100 years, things could change... Like Feynman said, we don't really understand quantum mechanics.
Why is everyone so confused? Basically, the only new principle involved is that instead of power being generated by the relative motion of conductors and fluxes, it’s produced by the modial interaction of magneto-reluctance and capacitive diractance. The original machine had a base plate of prefabulated amulite, surmounted by a malleable logarithmic casing in such a way that the two spurving bearings were in a direct line with the panametric fan. The lineup consisted simply of six hydrocoptic marzelvanes, so fitted to the ambifacient lunar waneshaft that sidefumbling was effectively prevented. The main winding was of the normal lotus o-deltoid type placed in panendermic semiboloid slots of the stator, every seventh conductor being connected by a non-reversible tremie pipe to the differential girdlespring on the ‘up’ end of the grammeters. Moreover, whenever fluorescence score motion is required, it may also be employed in conjunction with a drawn reciprocation dingle arm to reduce sinusoidal depleneration.
And people saying this video was complicated. What if Derek told us all of this with these technical words? I know quite some stuff about physics but I have no idea what a turboencabulator even is.
Originally, the metre was defined as 1/10 million of the meridian from the north pole over Paris to the equator. And that is slightly longer than the second pendulum which is also said to be about 1m long.
Up until now, I was able to understand almost every video of Veritasium I watched, but this goes waaaay over my head. Maybe because It's about electricity
It is awesome that there is a science channel that does not try to overly popularize a subject. For people with knowledge on physics this was extremely informative. I can now easily describe how the kilogram is defined. Thank you!
As a Metrologist, I want to commend you on your selective obfuscation of the TL;DR aspect of physics which are crucial to this measurement! Needless to say, with this method we are able to balance almost every source of error to such a high degree that once we've defined Planck's constant, we will know when we are off in our measurement when it doesn't agree with with the determined value of that constant (a little inside joke). That being said, if the universal constants are changing, we're all doomed because we will have no way of knowing! Which goes to the question begged in one of your other videos; are we expanding with the universe... how would we know? Since nowadays we measure the value of everything by physical constants, if they changed, we would never know, at least not by our standards because they're all relative to one another. However, these constants affect other behaviors in physics, and since everything is related; perhaps we would be able to determine that something(s) was(were) changing; but determining what exactly and why... well, with hope, we might not be around to know.
@@gyurhanaziz7676 Since α = (e^2) / (4πε₀ħc). We don't know exactly how each of these constant variables affects the others, only that this relationship exists. While measuring α, would allow us to detect if one of the other constants changed, since we do not know why this relationship exists, if the change of one affected the change of all of them, 'α' would still remain the same. If that's true, then perhaps nothing would affect us, and we'd never know they were changing. Since we don't know what the lower or upper limits of these are, we wouldn't see the catastrophe coming until one of the two limits surpassed the primary reason that these values are what they are. IOW, why does this relationship exist? To know so much, only to discover we know so little. This is the real problem. OTOH, I think our paradigm is changing with our perception of the ADS/CFT correspondence; and if we can fully get outside of our monkey brain to comprehend these things beyond "banana", like why these values are what they are. Then, we'll be masters of the universe. ;-) But, yes, I agree. If we measure the fine structure constant, essentially if only one constant changes we would see this, as long as we can obtain a high enough significance in our current measurements. And yes, if one of them did change, this would define an observation of the catastrophe in progress, if we are lucky enough to still be here. OTOH, if this relationship is stable, we could also have the opportunity to watch it evolve over time, if the behavior of the other variables (sic) forces them into alignment to negate any effect. This would be presuming that ADS is the built-in error correction to the quantum computer of the universe.
This is brilliant. The gravimeter doesn't even require calibration per se. It needs to be only traced back to distance and time, not easy to do using frequency standard and laser interferometry. Brilliant.
Affun Zee At least it helps that you're curious enough to watch his videos. Satisfying your curiosity and getting a general idea on the scientific process will help you tons(see what I did there) later in school.
This was all in my A2 Physics exams (including the hall effect), where we were asked to derive each of the individual equations stated in the video, except for the josephson effect...
I didn't really understand much like I know what you mean, but I really just like how you talk and I like listening to it while doing something. The talks and your voice are soothing, really
I don't get it. But I haven't slept in 5 yrs, Im drunk and I just got shot. If there are any spelling errors please excuse them as English is my 8th language.
Why you say like dat? Sorry mistakes if for engrish is my2189182u9872198728787928792187921872198721781278127377983278923329832980328902382398329839034904980879549874389034980894894th langiuge
Kilogram from wikipedia : The kilogram is defined in terms of three fundamental physical constants: The speed of light c, a specific atomic transition frequency ΔνCs, and the Planck constant h. The formal definition is: 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 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.[3][4] This definition makes the kilogram consistent with the older definitions: the mass remains within 30 ppm of the mass of one litre of water en.wikipedia.org/wiki/Kilogram
You should reference a RU-vidr named Practical Engineering, cuz he made his own watt balance using wood and as the structural material. It was pretty cool! He wanted to accurately measure the weight of what he thought was 20 kg, but it was actually 19.6 kg. I don't really know how accurate his machine is, considering it's not meant to be accurate, but it's still cool just despite that!
You should do a video about the discrepancies between the Kibble balance and the Avogadro project. As you might have heard the measurements never had time to completely settle before the deadline to fix the constants so that left a discrepancy between the two constants with regards to the kilogram based on what method you use to realize it.
I heard an interesting NIST talk related to this. Scientists/Engineers at NIST are having to determine how much water is trapped on the surface of the platinum standard KG weights. All of the international standards are stored (or weighed) in air, so their weight includes the water stuck to their surface. They become lighter in put in a vacuum and the water is desorbed (outside of the buoyancy affect of air) . I think the mass of water was on the order of of micro grams, so a significant amount relative to the part per billion accuracy. The folks at NIST are very remarkable, and really good at chasing down any possible uncertainty.
Veritasium, that's a brilliant job in explanation!! What we need is a children's book explaning this, so young students learn to appreciate what 'exactly' are we speaking of when we talk about physics ( the basic building blocks), instead of just learning to solve equations. Will work wonders for many!!!
I dont understand any of those words, my brain can't handle it, but idk why but i still love watching this kind of video, even tho i dont understand it lmao
We can, as a stop gap measure, implement the Metric Mile(=1500m) on all of our interstate highways (and government roads). This metric mile would approximate 0.93 standard miles. Then this metric mile could be divided into 5000 metric feet. The metric foot will equal exactly 30cm or 11.8 inches.
"That foam of quantum fluctuations which binds the universe together and allows the wormholes of the farcaster, the bridges of the fatline transmissions! The “hotline” which impossibly sends messages between two photons fleeing in opposite directions!" -Flashback dealer
do y'all know the way. one inch = the distance from the tip of your finger to the first joint one foot = your rist to the bend of your elbow one mile = the average distance you walk in 1/3 of an hour
ah niu Actually, all units used in the USA are "scaled" from metric standards. The USA's NIST had highly accurate first tier measurements for all metric units, which got translated into physical second tier standards (in metric), then got "scaled" to USA traditional units. That's why, if you look for the exact definition / standard of USA units, you'll find out that every single one of them are defined against metric (e.g., 1 inch = 25.4mm, 1 pound = 0.4536kg, and so on)
Yes. Although to be fair nobody uses the SI to its fullest possible extent like it should be (e.g. a fair number of non-SI units continue to be used along side the rest like "metric horsepowers" and "kgf", "astronomical unit", hours and minutes, etc. Really about the only two non-SI units you cannot totally do away with are the day and year, and even then only for the scheduling calendar to schedule things at times when people are awake, they are not needed to actually _measure_ anything. _Everything_ else can be replaced with SI, plus that 1 day = 86.4 ks, and 1 year = 31.5576 Ms as a standard value. (The last is 1 "Julian year", also called an "annum" (a), and is the same as 365.25 86.4 ks days.)). But nonetheless the US is really goofed up by lagging behind in the use of even the two other common SI units (kg and m, and their prefixed scaled forms) in everyday life. I doubt if anyone would really bat much if we changed all "1 lb" items to "500 grams". Would still feel pretty much the same, and thus it's not difficult to transition from thinking in "pounds" to "500 gram increments", esp. given that intuition is far from precise. Actually they'd get a little bit more for their buck because it's ~47 g heavier. But everyone FEARS that it'll be horrible, thus they don't want it. Just like how they FEAR that if we make a sensible healthcare system, they're going to lose out bad. When really, there are countries who do better healthcare than the US for a fraction of the cost per capita.
We have, because the imperial system is defined by the international system... we're just making things a lot more harder than what they should be. You know, the American way: we could give superior education to everyone, health care to everyone, fix our infrastructure, invest in green energy and stop spending in imperialism and wars that nobody wants, but that would make thing too easy for the American way.
Ebon Hawk Mass, not weight. Mass does not depend on gravity. A triple beam balance will give the same reading under any gravity (provided it is not near zero)
Generally, when metrologists pick a standard, you can be sure that they have a very high precision in all steps involved in the process. For your method, note that the density of water varies e.g. with temperature, and that temperature is really hard to measure with precision. One also has to pay attention to the isotope content in the water - a little bit of deuterium would throw things off.
I am glad you went into as much detail as you did since even though some might not know everything that you talked about, if you skipped it all then nobody would have understood it whether they knew what you were talking about or not :)
It would, but this watt balance beat the silicon sphere in measurement uncertainty. Measurement uncertainty is defined by how much do we not know. It's very certain that silicon sphere might weight exactly 1kg but something that weights 30 micro gram more or less would also be measured as 1 kg. This watt meter takes that unknown to 13 micro gram
It's actually pretty smart. You take a physical object that you define has your lenght. Then you measure a constant with this lenght (speed of light). Now you have a number. Should the physical object change in any kind (lenght contraction due to temperature change for instance or some internal structure effects), you can always resort to the constant that you know is never changing. You can do the same with any other constant like the Planck constant h and so to say "store" a defined size in a fundamental physical law. And should we ever meet aliens, we can tell them: our kg is this of h and our meter is that of c, and they can instantly convert their measurement units to ours.
No. Watch the whole d-*-*-*- thing!! and eat all your vegetables [unless you shouldn't]!!! I'm joking, I'm experience the humor/comedy version of sarchoticism right now😥 It's like being werewolf, but instead, you turn into an internet troll😭
I'm wondering what is actually happening with the Kgs: is the standard Kg losing mass, are the reference Kgs gaining, or some combination (which of the Kgs happens to be the most accurate)?
Quote: In a medium, light usually does not propagate at a speed equal to c; further, different types of light wave will travel at different speeds. The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity
Ah, yes, the old "stop chopping off 'in a vacuum'". Massless things only exist at the speed where they don't experience time. Would you like it better if I called it "untimely velocity magnitude" instead?
@@Improbabilities umm i doesnt matter what you call it but its a bit hard to measure a constant velocity that isnt constant to get an accurate millimeter for my ruler
