I'm one of the weird people that actually really likes imperial units. For instance:
1 foot -- base 12. This is a superior base to 10. It can be easily divided into 4ths, 3rd, and 2nds. Base 10 can only easily be divided into 2nds.
1 inch -- an easily identifiable unit of measure for smallish things. About the width of my thumb. A pretty good unit.
For low precision, inches become 1/2, 1/4, 1/8, 1/6, 1/64, etc. Each one is half the size of the previous one. I actually like this one a lot. An eight being half of a quarter is a really easy way to work with things when you're building stuff. Think about drilling a bolt hole in the center of a piece (half the width), or drilling two bolt holes with something in the center (divide those halves in half again) etc. Fractional is really good for building stuff.
For precision: thousands of an inch. Harder to visualize, but precise (has the same problems as mm imho). Millionths of an inch when you get into serious metrology.
Okay temperature: In imperial units:
0 = REALLY cold.
100 = REALLY hot.
50 = somewhere in the middle. Put on a sweater, but not dangerous.
100 = about the temperature of a human body.
Water boils at 212F and freezes at 32F. There are 180 degrees (degrees!) between freezing and boiling. 180 is, again, base 12. It's the 15th order of 12.
I actually love imperial units. I greatly prefer them to metric (even though I do use metric very frequently, and can see the appeal). I think I just actually prefer base 12 to base 10.
You're right - imperial is far superior for precise building or manufacturing work.
Take drill bits, for example. Obviously it's much easier to figure out that 11/32" is less than 3/8". Or is it more? No, I'm pretty sure I was right the first time. The metric ones with their 5.5mm, 6mm, 6.5mm sequencing are just too complicated to work with, in comparison. And half a millimeter isn't very precise - it's much bigger than 1/64". Well, a bit bigger. Let's not get into tenths of millimeters.
And at larger scales, of course, base 12 is much easier when it comes to dividing distances. Taking a distance of 2'7" and dividing it by three in your head is much easier than dividing 79cm by three, because... well, 2' divided by three is 8", obviously. If you need to be sure, just tap it into a calculator. That supports base 12...
Anyway, you'll quickly determine that it's 10 1/3", which is much more precise than 26.3333cm. Now I just need to subtract the radii of these two 5/16" holes from that, which is easy - imagine trying to subtract 8mm from 26.3333cm! What folly.
I understand, that you know the metric system, and, judging by your reasoning for your love for the imperial system, I understand, that you know what you are talking about (better than me). So, please, do not understand my comment as wanting to advise you! It's just, that I found this (on the web, one day) to express so much the way I (having grown up with the metric system) feel about it:
"In metric, one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade -- which is 1 percent of the difference between its freezing point and its boiling point. An amount of hydrogen weighing the same amount has exactly one mole of atoms in it.
Whereas in the American system, the answer to 'How much energy does it take to boil a room-temperature gallon of water?' is 'Go fuck yourself', because you can't directly relate any of those quantities."
Hmm, good for usage you say. Ok, let's stick to "standard" imperial units. How many feet in a yard? Yards in a mile? What the hell is a quart? And since base 12 is great, what is 12 feet called? 144 feet? A 12th of an inch?
Or, ounces: How many ounces in a gallon? A pound? And how many _kinds_ of ounces are there, anyways?
You are definitely (and thankfully) not the norm. Imperial units are awful. They're more ... human, maybe, in that a foot is about one human foot long, and that an inch is about one human thumb width, and how 0F feels "pretty cold" and 100F feels "pretty hot", and to me the charm of imperial units begins and ends right there.
Those are literally the only redeemable qualities about imperial units, and they have nothing at all to do with their utility as a tool for measurement.
I am glad that you like them. Use them all you like. I won't.
While I agree that in many ways imperial is better than metric in the way that you mention. It is absolutely atrocious when it comes to weight and volume. A gallon is still a base 10 unit of measure of water (10 pounds of water). Then only after that, is it in base 8 rather than maintaining that base 12 consistency.
Then if you look at imperial units of weight, it deviates away from base 12 again. It counts upwards from a pound using base 14 with stone and ton. And then when counting downwards it uses base 16 for a little bit with ounces, followed by out of nowhere throwing in a 1/7000 for a grain unit.
Even ignoring the scientific applications, none of this is easier for visualization purposes than grams or kilograms, nor is it all that useful for volumetric units either with maybe the exception of using cups instead of milliliters for cooking.
I understand some of what you say, but the point of standard unit is not so that people can choose which unit they like. It's to make sure everyone uses the same ones. If all but a few countries used imperial as their standard measure then I'd go for it. But right now it's the odd one out. Itu mostly survived only thanks to being associated with an economic superpower, so international companies can't afford to ignore it.
Yeah, no. You're just suffering from Stockholm Syndrome or being thinly ironic.
People have absolutely no problem associating numbers to temperature sensations in C. And actually people can objectively feel temperature differences from around 2C/5F so in that way C is superior to F, 1F difference is meaningless.
It's true that (for example) a third of a metre isn't expressible accurately in decimetres, but you can always just say (continuing this specific example) "a third of a metre". Nobody will be confused about what you mean.
This is however perhaps a good argument in favour of non-decimal currency.
Base 12 is more convenient than base 10. But that argument really only works if numbers were written in base 12. They're not, though, and that isn't changing any time soon. As a result, Imperial has to deal with two bases - the units themselves are defined base 12 (more or less; it's not really consistent e.g. with volume), but then you still have to do arithmetic in base 10.
So, until such time as we switch to base 12 for all numbers, metric is superior, because it is simpler.
No matter what is suggested, no matter how much better the alternative, there will always be a group of contrary people. Look at flat earthers. Look at anti-vaxers.
You're just familiar with it - as somebody who has grown up with the metric system, I feel exactly the same affection about it, and to me imperial units feel stupid, unworkable and old fashioned.
I think this is the biggest problem with metric/imperial arguments - most of it is actually based on emotional attachment deep down.
I hadn't thought of some of these advantages. Some are subjective, but it's hard to deny the intuitive nature of others. I say bring back the span and the rod as well.
I'm glad you made this point, because I am the one that usually does and gets hammered for daring to even hint that imperial might not be totally insane! The temperature one I've always found compelling. Most humans only rarely experience temperatures outside of 0-100F. That makes sense to me. Celsius makes little sense, except for 0 being when water freezes. It compacts the scale too much for everyday use.
However, beyond basic human usage, I quickly switch to metric for anything involving actual math: simulation, science, finance, etc.
A "cup" is about what a normal drink is. A liter is an insane amount of liquid for everyday use. I don't sit down and drink a liter of wine, I have a cup of wine.
Divisibility by 12 could have benefits when working with small numbers, but on the other hand multiplying by 12 doesnt sound like operation you can do easily from top of your head...
0 degrees Farenheit is also the temperature salt stops freezing water. It is a good thing to remember when you are wondering about driving on snowy and icy roads.
Just as a side note, the US system gets worse and worse when you look beyond the everyday units of measure.
Sure, inches are great, but below 1/4", screws are in a numbered system (higher number is larger) while the corresponding drill bits are in a different numbered system (higher number is smaller) or lettered (A to Z). Wire and sheet metal gage numbers are still different.
F is not superior to C, your argument for it makes very little sense, even from a plain human "everyday" (non-scientific) point of view. Can anyone sense when the temperature changes by a single degree in F? I doubt it. With C you have a chance. With C when it's below zero you know there could be snow and ice.
Each set of 10 degrees in C is a pretty clear temperature range.
30-40 scorching.
20-30 hot.
10-20 warm.
0-10 cool.
-10 to 0: cold
You should be careful about the term "imperial". US customary units do not always match the old British "imperial" units. A US fluid pint is significantly smaller than an Imperial pint, for example.
Celsius and Fahrenheit may be use for some thing, but I think kelvin is a good system, even if others are use for other purposes sometimes (such as Fahrenheit for oven temperatures).
I feel like imperial units are human units. they are units used on a human scale, where as metric are more 'computer'. example: a human really cant look at something and divide it by 10 very well, but 1/3, 1/2, 1/4, very easy to do. the sizes makes human sense, like a foot being about a human foot, etc.
Most probably because you grew up with it. I’m pretty sure you think the same about your religion, nation, race ... but be sure eveybody else in the world may think the same of their own. And they’d be right too.
What I personally find disturbing is how irrational positions such as yours are commonly accepted in a supposedly advanced society. It leads to a pretty bumpy road, time and time again.
I like to commend my American friends for their undying loyalty to the memory of the Empire. U.S. customary units are derived from units that helped the British conquer the world, but even the British themselves have shamelessly abandoned them for the units of a filthy, monarch-less republic. It's good to see that Americans still subconsciously yearn for the firm ruling hand of their rightful Queen.
As of today, they are both implemented using fundamental constants. ;-)
But indeed, most people worldwide are surprised when you tell them that there is no standard inch or standard pound sitting in a vault somewhere. Most machines, and most design software, have a button that switches between US and metric, and the machine itself doesn't care. More and more new products in the US use metric fasteners unless it's for something where a standard applies to exactly one thing, such as spark plug thread. I have used my metric tools more than my US tools in the process of doing repairs around the house, on my car, and my bikes.
One fastener on my bike uses Whitworth threads.
For all intents and purposes, it has ceased to matter.
Nope, because we don't use the Imperial system, though. We use American Standard Units. They happen to be just like the Imperial units, except they have more freedom.
It's stunning to see people debating "ease-of-understanding" of the base 12 imperial system while at the same time happily using a decimal based currency (nearly?) all over the world.
It's easy to understand construction and cooking concepts in imperial? But you just used a decimal based currency to buy the materials for the said uses, and could easily add up the costs of those materials in your head instead of staring blankly at the cashier who was trying to add 77 shillings and 23 half-crowns.
Can you imagine the confusion? Having the same word mean a different amount of something would cause a lot of misunderstanding. Saying "This car weighs 2200 poundsm" have two different meanings depending on the year you said it sounds awful.
The new metric definitions work because they don't change the actual amount, they just change the way the amount is defined. (Natural constant vs reference weight)
How would you use the new definition to calibrate instruments? My current understanding is that there is a lineage of artifacts calibrated against another artifact until one of those was calibrated against the one true artifact. So how would NIST or another certifying source say that my 1kg standard is 1kg +/- tolerance?
Is it anyone with a kibble balance can now certify calibrations? How do you know your kibble balance is as accurate as the next guy's kibble balance?
Essentially this brings it one more step away from using another artifact for calibrating things. Instead this lets us define the kilogram against what we believe are universal constants, in this case properties about the electromagnetic force.
It's much simpler to understand looking at it with a watt balance, even though it's not going to be as precise or accurate as a kibble balance [1]. Basically now anyone with access to a kibble balance and the right set of numbers/information can make an exact 1kg object.
Or potentially more usefully, ascertain an accurate measurement of how closely a given measuring device is to the target to calibrate it's use in actual measurements (outside of the expensive validation mechanisms).
I'm pretty sure a watt balance and a Kibble balance are the same thing. Regardless, that YouTube video is so good! I was just about to post the same link.
It will still mostly work the same way, except that instead of someone having the "one true artifact", anyone with enough equipment can measure their kilogram against natural constants and know it's correct.
It means the right answer is freely available to anyone (with a bunch of scientific equipment).
The pictures in that article about NIST reminds me of the adage, "The smaller the measurement, the bigger the lab."
I like to use metrology labs as an example of something people often take for granted (measuring things) and showing how deep that invisible rabbit hole goes.
The NIST explanation of Kibble balance calibration includes this:
> Everything on the right side of that equation can be determined to extraordinary precision: The current and voltage by using quantum-electrical effects that are measurable on laboratory instruments; the local gravitational field by using an ultra-sensitive, on-site device called an absolute gravimeter; and the velocity by tracking the coil's motion with laser interferometry, which operates at the scale of the wavelength of the laser light.
Current is measured in amperes, derived from the charge (in coulombs, defined from the charge of a proton) and time (in seconds, defined from the vibration of a Cs atom). Gravitational acceleration is measured in ms^-2, derived from length (in metres, defined from the distance travelled by light in a vacuum in a second) and time. Velocity is also derived from length and time.
With these new defined constants (including the Planck constant), all of the instruments could now be calibrated by observing natural phenomena and a whole lot of counting.
This is probably the dumbest thing I'll type on HN.
In university I just gave up trying to understand why we even needed the Avogadro constant / mole as a fundamental constant. It still confuses me. Why have a difference between molar mass and mass? Why couldn't it just be "1" and everything else change around it?
Understanding mass in molar terms is necessary to do a lot of chemistry correctly. The mole is effectively a count of the number of molecules kicking about, although the count is large enough that terms like "quadrillion" don't cut it. (One mole is about 600 sextillion molecules). Knowing how many molecules are around lets you actually compute how much stuff can react in a given chemical environment, and other aspects of chemistry end up being pretty related to molecule counts. Vanilla mass doesn't cut it since an atom of iodine weighs about 6.6 times that of fluorine but can still only react with one other molecule.
The flip side is that the molecular count is less useful to us in the everyday world. We can gauge the weight of a kilogram much more than we can gauge a septillion molecules. And if we're trying to figure out how much stuff a shelf can hold before it collapses, it's the weight that matters, not the actual molecular count. (Note for pedants: in the familiar environment of Earth's surface, mass and weight can be treated as the same quantity in most cases.)
So mass and molecular count are both very important quantities that have importance in different fields of science, and they don't have a trivial relationship to each other. Avogadro's constant and molar mass is a way to express their relationship.
trying to use kg instead of moles when calculating a chemical reaction would be like trying to set up a speed dating event by taking the weights of all the men and women instead of matching them up pairwise. Sometimes it is much easier to calculate based on scalar quantity than it is to calculate based on mass.
My understanding is that the cause is error propagation. We can measure certain kind of masses really accurately in unified atomic mass unit. With better relative precision than the Avogadro constant. But if we used kilograms to write down these quantities then they would carry the error of the Avogadro constant needlessly.
Edit: I think your question boils down to "Why do we have two separate units for mass, u and kg, connected by the Avogadro constant?" Most answers dismiss your original question as Avogadro constant is not a unit. But u is a unit and it's the point why we have this constant.
Edit2: To further emphasize my point look at the mass of neutron[1]. It's listed both in kg and u. Note the number of decimal places.
Right, I get that, and if anything I feel less dumb now that I've asked it publicly and people seem to think that it's a non-dumb question, but when talking about fundamental constants I understand there is a practical nature to it all, but just as we have a nano-meter and a light-year I figured we'd have the same for mass.
Why do I need both kg and u as fundamental constants?
I believe the comments here have answered it. It isn't something weird, like quantum gravity or some such. If I understand everyone correctly it's just a practical decision we made at some point because we didn't want mass to be in u and that's that.
In a meta-sense, I don't think your question is dumb at all.
There's a complicated technical topic which you're still not understanding. There's no indication it's a question you could easily answer yourself, and you're posting it in a forum of people likely to find the topic interesting, some of whom might give an answer that clicks for you.
As others have noted, knowing the count of entities (note: not atoms, entities - i.e. it can also be molecules) in relation to actual mass is very useful for the physical sciences - at a molecular level the quantities of molecules and atoms interacting matter, not their masses - but mass is the unit I do experiments with.
EDIT: A simple example would be if you were trying to make water - H2O, from hydrogen (H2) and oxygen (O2). The molar ratio is 2:1 - but in doing a practical synthesis, that doesn't tell me how much mass/volume of gases to actually mix up. Avogadro's number and molar mass is what I need to turn those into practical units to work with.
> the Avogadro number was initially defined by Jean Baptiste Perrin as the number of atoms in one gram-molecule of atomic hydrogen, meaning one gram of hydrogen. (from Wikipedia)
(It's since been refined to be 12 grams of carbon-12.)
So a mole is defined to be approximately one gram worth of protons and neutrons. We use it because grams are a significantly easier unit of mass for humans to work with, than like individual particles.
Historically, the mole predates the acceptance of atomic theory. Stoichiometry of various reactions let you work out that there was some mass of oxygen that would entirely react with some mass of carbon to form carbon monoxide. They didn't have the same masses, but the relative amounts for each element were constant (or small integer multiples, such as twice as much oxygen to carbon for CO_2).
So Dalton took the lightest one, hydrogen, and defined a mole as the stoichiometric amount equivalent to that in 1g of hydrogen. Looked at that way, it's a pretty solid choice.
In chemistry, the molar “mass” plays a more important role than the mass proper. Why has its unit not been chosen to be equal to 1? For the same reason as why the gram is not defined to be the mass of, say, proton. (Chemistry doesn’t normally deal with single molecules.)
In my opinion it is because a mole is a numerical amount of atoms vs the mass of the substance, so it makes reactions, formulas, and measurements easier to determine. Avogadro's number is useful just as a baseline to use (number of carbon-12 atoms in 12 grams of carbon-12), like there are 12 inches in a foot or 100 centimeters in a meter...
I don't believe the Avogadro constant needs to be an SI unit. It's like having 12 as an SI unit, or a million, or 1. Sure, it's a useful constant scaling factor, but it doesn't need to be canonized at the heart of the SI system. It doesn't actually express anything fundamental about how we measure our universe.
And if nothing else, it can be derived: a mole is the number of atoms in a kilogram of carbon-12. Done.
Isn't this something essentially tautological though?
When we discuss the mass of a neutron and we say "one neutron weighs one u" then we discuss the mass of an electron and we say "one electron is 5.4858×10−4 u" and "one proton is 1.0072764 u" then we add them up and say "one hydrogen atom is 1.00794 u while one helium atom is 4.002602" (forgetting some complications for a moment) are we not just summing likes?
Or is it just that since mass is defined in Planck and time / distance terms that we need to relate it to counts of things? Theres a gap there I don't understand. Can we not just say "we measured a proton's mass and it is u"? Am I making a jump there?
The one that made it click for me as incredibly useful was Avogrado's Law (now part of the Ideal Gas Law):
> Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.
This law, for example, explains why hot air rises. Take two equal quanties of the same gas at the same pressure. They will have the same volume. Now, heat one quantity of gas. By this law, that gas will have a larger volume at the same pressure. Because it has the same amount of mass distributed over a larger volume, it must be less dense. Therefore, it rises.
> By this law, that gas will have a larger volume at the same pressure.
It will have larger volume, but that is not implied by Avogadro's law. That law is about the surprising property of all gases: no matter the chemical nature of the gases, if they all have same T and P, they all will have same number of molecules per unit volume.
No I agree, it seems stupid. What we did is take a block of metal and call it a kilogram, figure out how many atoms are in 1/1000 of it (a gram) and call that a mole. What we should do is redefine the gram to be whatever 1e10 atoms of Hydrogen weighs, or something similar. When I read the headline I thought thats what they did, and I admit first reaction was "oh god I'm going to be dealing with conversions and associated errors for the rest of my life".
> What we should do is redefine the gram to be whatever 1e10 atoms of Hydrogen weighs, or something similar.
That was actually an alternative proposal for redefining the kg. The kg would have been 1000/28 the weight of a mole of silicon-28; you could build a sample by counting 6.023x10^26/28 atoms of silicon-28, and making a sphere out of them.
Initially the watt balance seemed to be less precise than atom counting, but then it was improved to a point where defining the kg on top of the mole became less convenient than the definition they are adopting now.
We need a means of converting mass to number of atoms so that we can predict how much mass of a specific product will be formed, what the limiting reägent will be, &c.
It also helps to define concentrations based on number of moles in a L of solvent (Molarity vs g/L) for the same reason.
> why we even needed the Avogadro constant / mole as a fundamental constant(...?)
It serves as a link between human-scale and atomic-scale observations, classically needed for chemistry performed on Earth by humans. This link must exist, as others mentioned, for stoichiometric calculations (e.g. air/gas mixture in a internal combustion engine). For much of modern scientific history, it was deemed useful to scale into an easily eye-visible human scale (the gram). [0]
The number of things in a mole is arbitrary. It's a dimensionless unit. However, since many things are already measured in moles in chemistry, there's no real reason to remove it. Dealing with numbers on a more practical macroscopic scale is probably more convenient than dealing with large powers of 10.
Well, now you could do that. At least you could next March when these rules take affect. But before you could not because the conversion between atomic mass and SI/kg mass depended on that experimental constant. Two mass systems were required because we couldn’t conver between them with atomic accuracy.
I thought it was just a ratio. Mass per mole. I admit I have never used this in my day to day life and college was 20 years ago. So maybe I am clueless.
Nah, I think that's just it. It's easier to write down certain calculations in mole in a chemical context, because you're concerned with atoms reacting with each other. You don't have 12 grams of carbon and 4 grams of hydrogen, but 1 mole of carbon and 4 mole of hydrogen.
For the same reason that we use both temperature and energy and find them both useful. We can talk of the energy of an electron. On the other hand, temperature, is an statistical property defined for many particles.
Using mole (based on Avogadro constant) makes it easier to do statistical mechanics, but it's not a microscopic property like mass.
Mostly yes, it does seem over-stated. I guess if you squint "wide-reaching" does not necessarily mean "important" just, you know, "wide-reaching". Like the "wide-reaching" effect of dropping a pebble into an otherwise undisturbed swimming pool maybe? The ripples go pretty far, they don't really matter, but they do go far.
With the old definitions, the values of the known constants were just approximations, but now that the unit is defined based on the constants, we can consider the constant as being the exact value, no matter how imprecise it was when it was measured using old definitions of the units.
I don't know about trade, but kilo standards were deviating by tens of micrograms from eachother, some things are sold at prices which warrant accounting for those micrograms, so a completely stable international definition seems helpful.
Certain types of scientific instrument will need to be recalibrated to meet the new definitions.
Is there any scale in the world that can measure a kilogram to within the accuracy of a microgram?
And if you buy a kilogram of something and they accidentally short you by a few micrograms, haven't you only overpaid by a few parts per billion? Even on a billion dollar order you've only overpaid by a few dollars...
I wish he would spend a bit more time exsplining were some of the constants come from, although that would probably make the video a bit weaker overall. Wasting time on such information.
Recently I have been thinking about if any of our units makes sense in cosmic perspective. Let's take speed of light for example. It's approximately 300000 km/s. But then what is a second? It's 1/60 of a minute which is 1/60 of an hour which is 1/24 of a day(and so it goes) and all those numbers are arbitrary. A day doesn't make any sense outside our planet anyway, I doubt that there is another celestial body in the universe that takes the same time to complete a rotation. Period of some natural phenomena (like atomic electron transition) sounds better as a unit but it's a really tiny period of time so we have to scale it to make it practical for us. We will use decimal numeral system to do that, another arbitrary choice. What if we had 12 fingers or 8? This can be extended to all kinds of measurements so I wonder if any of this would make sense to another civilization. What would a cosmic system of units would like? Any reading about this would be greatly appreciated.
The definition of a second isn't based on the Earth's motion, but some natural phenomena like you recommended. "The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom." [1]
You might be thinking along the lines of natural units [1] or even Planck units [2], where you set some fundamental constants to 1 and take it from there.
I would suggest that Planck units scaled by powers of 2 is the closest we can get to a cosmic system of units. The choice of binary is non-arbitrary as it's the smallest base that can be chosen and still provide scaling.
"The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom."
Readit News
(Fun fact: all the US customary units have been officially defined in terms of their metric counterparts since 1893: https://www.nist.gov/sites/default/files/documents/pml/wmd/m...)
1 foot -- base 12. This is a superior base to 10. It can be easily divided into 4ths, 3rd, and 2nds. Base 10 can only easily be divided into 2nds.
1 inch -- an easily identifiable unit of measure for smallish things. About the width of my thumb. A pretty good unit.
For low precision, inches become 1/2, 1/4, 1/8, 1/6, 1/64, etc. Each one is half the size of the previous one. I actually like this one a lot. An eight being half of a quarter is a really easy way to work with things when you're building stuff. Think about drilling a bolt hole in the center of a piece (half the width), or drilling two bolt holes with something in the center (divide those halves in half again) etc. Fractional is really good for building stuff.
For precision: thousands of an inch. Harder to visualize, but precise (has the same problems as mm imho). Millionths of an inch when you get into serious metrology.
Okay temperature: In imperial units:
0 = REALLY cold. 100 = REALLY hot. 50 = somewhere in the middle. Put on a sweater, but not dangerous.
100 = about the temperature of a human body.
Water boils at 212F and freezes at 32F. There are 180 degrees (degrees!) between freezing and boiling. 180 is, again, base 12. It's the 15th order of 12.
I actually love imperial units. I greatly prefer them to metric (even though I do use metric very frequently, and can see the appeal). I think I just actually prefer base 12 to base 10.
I also think that F is seriously superior to C.
Take drill bits, for example. Obviously it's much easier to figure out that 11/32" is less than 3/8". Or is it more? No, I'm pretty sure I was right the first time. The metric ones with their 5.5mm, 6mm, 6.5mm sequencing are just too complicated to work with, in comparison. And half a millimeter isn't very precise - it's much bigger than 1/64". Well, a bit bigger. Let's not get into tenths of millimeters.
And at larger scales, of course, base 12 is much easier when it comes to dividing distances. Taking a distance of 2'7" and dividing it by three in your head is much easier than dividing 79cm by three, because... well, 2' divided by three is 8", obviously. If you need to be sure, just tap it into a calculator. That supports base 12...
Anyway, you'll quickly determine that it's 10 1/3", which is much more precise than 26.3333cm. Now I just need to subtract the radii of these two 5/16" holes from that, which is easy - imagine trying to subtract 8mm from 26.3333cm! What folly.
"In metric, one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade -- which is 1 percent of the difference between its freezing point and its boiling point. An amount of hydrogen weighing the same amount has exactly one mole of atoms in it. Whereas in the American system, the answer to 'How much energy does it take to boil a room-temperature gallon of water?' is 'Go fuck yourself', because you can't directly relate any of those quantities."
From: "Wild Thing" by [Josh Bazell](https://en.wikipedia.org/wiki/Josh_Bazell).
Or, ounces: How many ounces in a gallon? A pound? And how many _kinds_ of ounces are there, anyways?
Fun fact: The term “ounce” is of Latin origin from the word “uncia” which means “a twelfth part.” http://www.differencebetween.net/science/mathematics-statist... So...what's an ounce a twelfth of?
Or, say, a pint. What's the definition of a pint?
Those are literally the only redeemable qualities about imperial units, and they have nothing at all to do with their utility as a tool for measurement.
I am glad that you like them. Use them all you like. I won't.
Then if you look at imperial units of weight, it deviates away from base 12 again. It counts upwards from a pound using base 14 with stone and ton. And then when counting downwards it uses base 16 for a little bit with ounces, followed by out of nowhere throwing in a 1/7000 for a grain unit.
Even ignoring the scientific applications, none of this is easier for visualization purposes than grams or kilograms, nor is it all that useful for volumetric units either with maybe the exception of using cups instead of milliliters for cooking.
Yeah, no. You're just suffering from Stockholm Syndrome or being thinly ironic.
People have absolutely no problem associating numbers to temperature sensations in C. And actually people can objectively feel temperature differences from around 2C/5F so in that way C is superior to F, 1F difference is meaningless.
This is however perhaps a good argument in favour of non-decimal currency.
So, until such time as we switch to base 12 for all numbers, metric is superior, because it is simpler.
I think this is the biggest problem with metric/imperial arguments - most of it is actually based on emotional attachment deep down.
10 C = you need a jacket
15-25 C = great outdoors temperatures
20 C = good house temperature in the winter
25 C = good house temperature in the summer
30 C = too hot to go out doing physical activity, good for a picnic or a day at the beach
35 C = too hot to go out, period
40 C = hot bath
100 C = boiling water
However, beyond basic human usage, I quickly switch to metric for anything involving actual math: simulation, science, finance, etc.
A "cup" is about what a normal drink is. A liter is an insane amount of liquid for everyday use. I don't sit down and drink a liter of wine, I have a cup of wine.
Sure, inches are great, but below 1/4", screws are in a numbered system (higher number is larger) while the corresponding drill bits are in a different numbered system (higher number is smaller) or lettered (A to Z). Wire and sheet metal gage numbers are still different.
An #8-32 thread takes a #29 tap drill...
https://www.lincolnmachine.com/tap_drill_chart.html
Each set of 10 degrees in C is a pretty clear temperature range. 30-40 scorching. 20-30 hot. 10-20 warm. 0-10 cool. -10 to 0: cold
Both are not metric though. Metric unit for temperature is kelvin.
The number of inches in a mile is harder to get than the number of millimeters in a kilometer or grams in a ton.
I'm glad I'm not the only person who thinks this way.
What I personally find disturbing is how irrational positions such as yours are commonly accepted in a supposedly advanced society. It leads to a pretty bumpy road, time and time again.
Note: Americans hate it when I do this.
But indeed, most people worldwide are surprised when you tell them that there is no standard inch or standard pound sitting in a vault somewhere. Most machines, and most design software, have a button that switches between US and metric, and the machine itself doesn't care. More and more new products in the US use metric fasteners unless it's for something where a standard applies to exactly one thing, such as spark plug thread. I have used my metric tools more than my US tools in the process of doing repairs around the house, on my car, and my bikes.
One fastener on my bike uses Whitworth threads.
For all intents and purposes, it has ceased to matter.
It's easy to understand construction and cooking concepts in imperial? But you just used a decimal based currency to buy the materials for the said uses, and could easily add up the costs of those materials in your head instead of staring blankly at the cashier who was trying to add 77 shillings and 23 half-crowns.
(the opposite of https://xkcd.com/2073)
The new metric definitions work because they don't change the actual amount, they just change the way the amount is defined. (Natural constant vs reference weight)
https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN...
Is it anyone with a kibble balance can now certify calibrations? How do you know your kibble balance is as accurate as the next guy's kibble balance?
https://www.nist.gov/si-redefinition/kilogram-kibble-balance
Edit: Found some information explaining this from NIST: https://www.nist.gov/si-redefinition/kilogram-disseminating-...
It's much simpler to understand looking at it with a watt balance, even though it's not going to be as precise or accurate as a kibble balance [1]. Basically now anyone with access to a kibble balance and the right set of numbers/information can make an exact 1kg object.
[1] https://www.youtube.com/watch?v=ewQkE8t0xgQ
It means the right answer is freely available to anyone (with a bunch of scientific equipment).
I like to use metrology labs as an example of something people often take for granted (measuring things) and showing how deep that invisible rabbit hole goes.
https://www.nist.gov/si-redefinition/nist-do-it-yourself-kib...
> Everything on the right side of that equation can be determined to extraordinary precision: The current and voltage by using quantum-electrical effects that are measurable on laboratory instruments; the local gravitational field by using an ultra-sensitive, on-site device called an absolute gravimeter; and the velocity by tracking the coil's motion with laser interferometry, which operates at the scale of the wavelength of the laser light.
Current is measured in amperes, derived from the charge (in coulombs, defined from the charge of a proton) and time (in seconds, defined from the vibration of a Cs atom). Gravitational acceleration is measured in ms^-2, derived from length (in metres, defined from the distance travelled by light in a vacuum in a second) and time. Velocity is also derived from length and time.
With these new defined constants (including the Planck constant), all of the instruments could now be calibrated by observing natural phenomena and a whole lot of counting.
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In university I just gave up trying to understand why we even needed the Avogadro constant / mole as a fundamental constant. It still confuses me. Why have a difference between molar mass and mass? Why couldn't it just be "1" and everything else change around it?
The flip side is that the molecular count is less useful to us in the everyday world. We can gauge the weight of a kilogram much more than we can gauge a septillion molecules. And if we're trying to figure out how much stuff a shelf can hold before it collapses, it's the weight that matters, not the actual molecular count. (Note for pedants: in the familiar environment of Earth's surface, mass and weight can be treated as the same quantity in most cases.)
So mass and molecular count are both very important quantities that have importance in different fields of science, and they don't have a trivial relationship to each other. Avogadro's constant and molar mass is a way to express their relationship.
Edit: I think your question boils down to "Why do we have two separate units for mass, u and kg, connected by the Avogadro constant?" Most answers dismiss your original question as Avogadro constant is not a unit. But u is a unit and it's the point why we have this constant.
Edit2: To further emphasize my point look at the mass of neutron[1]. It's listed both in kg and u. Note the number of decimal places.
[1] https://en.wikipedia.org/wiki/Neutron
Why do I need both kg and u as fundamental constants?
I believe the comments here have answered it. It isn't something weird, like quantum gravity or some such. If I understand everyone correctly it's just a practical decision we made at some point because we didn't want mass to be in u and that's that.
I feel better about it now.
There's a complicated technical topic which you're still not understanding. There's no indication it's a question you could easily answer yourself, and you're posting it in a forum of people likely to find the topic interesting, some of whom might give an answer that clicks for you.
Well done, IMHO.
EDIT: A simple example would be if you were trying to make water - H2O, from hydrogen (H2) and oxygen (O2). The molar ratio is 2:1 - but in doing a practical synthesis, that doesn't tell me how much mass/volume of gases to actually mix up. Avogadro's number and molar mass is what I need to turn those into practical units to work with.
> the Avogadro number was initially defined by Jean Baptiste Perrin as the number of atoms in one gram-molecule of atomic hydrogen, meaning one gram of hydrogen. (from Wikipedia)
(It's since been refined to be 12 grams of carbon-12.)
So a mole is defined to be approximately one gram worth of protons and neutrons. We use it because grams are a significantly easier unit of mass for humans to work with, than like individual particles.
So Dalton took the lightest one, hydrogen, and defined a mole as the stoichiometric amount equivalent to that in 1g of hydrogen. Looked at that way, it's a pretty solid choice.
And if nothing else, it can be derived: a mole is the number of atoms in a kilogram of carbon-12. Done.
No longer is. Not quite.
When we discuss the mass of a neutron and we say "one neutron weighs one u" then we discuss the mass of an electron and we say "one electron is 5.4858×10−4 u" and "one proton is 1.0072764 u" then we add them up and say "one hydrogen atom is 1.00794 u while one helium atom is 4.002602" (forgetting some complications for a moment) are we not just summing likes?
Or is it just that since mass is defined in Planck and time / distance terms that we need to relate it to counts of things? Theres a gap there I don't understand. Can we not just say "we measured a proton's mass and it is u"? Am I making a jump there?
> Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.
This law, for example, explains why hot air rises. Take two equal quanties of the same gas at the same pressure. They will have the same volume. Now, heat one quantity of gas. By this law, that gas will have a larger volume at the same pressure. Because it has the same amount of mass distributed over a larger volume, it must be less dense. Therefore, it rises.
It will have larger volume, but that is not implied by Avogadro's law. That law is about the surprising property of all gases: no matter the chemical nature of the gases, if they all have same T and P, they all will have same number of molecules per unit volume.
The law as quoted doesn't say what happens when the temperature change. Maybe it gets more dense? Be more specific.
Disclaimer: I took high school chem, that's it.
Cf binding energy, electron excitation, E=mc^2 (the m there is m0, the rest mass; the full equation includes the momentum and "relativistic mass").
The situation is actually worse for hydrogen (cf hydrogen bonding).
http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.htm... is a pretty coherent and readable approach to the subject.
That was actually an alternative proposal for redefining the kg. The kg would have been 1000/28 the weight of a mole of silicon-28; you could build a sample by counting 6.023x10^26/28 atoms of silicon-28, and making a sphere out of them.
Initially the watt balance seemed to be less precise than atom counting, but then it was improved to a point where defining the kg on top of the mole became less convenient than the definition they are adopting now.
We need a means of converting mass to number of atoms so that we can predict how much mass of a specific product will be formed, what the limiting reägent will be, &c.
It also helps to define concentrations based on number of moles in a L of solvent (Molarity vs g/L) for the same reason.
It serves as a link between human-scale and atomic-scale observations, classically needed for chemistry performed on Earth by humans. This link must exist, as others mentioned, for stoichiometric calculations (e.g. air/gas mixture in a internal combustion engine). For much of modern scientific history, it was deemed useful to scale into an easily eye-visible human scale (the gram). [0]
[0] https://en.wikipedia.org/wiki/Avogadro_constant#General_role...
https://en.wikipedia.org/wiki/Mole_(unit)#Criticism
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Because the SI system is redundant anyway one constant more or less doesn’t matter much.
If you want a truly minimalist system you can use CGM or MKS.
Using mole (based on Avogadro constant) makes it easier to do statistical mechanics, but it's not a microscopic property like mass.
"the new changes will have wide-reaching impact in science, technology, trade, health and the environment, among many other sectors."
Am I missing something?
Certain types of scientific instrument will need to be recalibrated to meet the new definitions.
And if you buy a kilogram of something and they accidentally short you by a few micrograms, haven't you only overpaid by a few parts per billion? Even on a billion dollar order you've only overpaid by a few dollars...
[0] https://youtu.be/c_e1wITe_ig
[1] https://www.scientificamerican.com/article/how-does-one-arri...
[1]: https://en.wikipedia.org/wiki/Natural_units [2]: https://en.wikipedia.org/wiki/Planck_units
Speed has an obvious unit which is the speed of light (in a vacuum), which seems to be the same everywhere.
All the others are a bit more arbitrary I guess.
I would suggest that Planck units scaled by powers of 2 is the closest we can get to a cosmic system of units. The choice of binary is non-arbitrary as it's the smallest base that can be chosen and still provide scaling.