RawWork
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How to find or define units?
Let's say I am in jungle and need to measure 1 meter exactly, how?
Or let's say world war 3 happens and somehow it exactly hits all devices and stuff that units can be defined from or compared to (even papers,
bottles, sim cards...), how to redefine then?
I heard on wikipedia something called interferometry, but that sound complicated and impossible to build before already having something.
I am not talking only about meter, but any unit like g, mL, V, A, W...
I somehow don't believe in copy paste of units, even from standard stuff, as one nanometer more or less can cause catastrophic failure of let's say
electronics. How to measure units precisely? Without anything advanced.
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XeonTheMGPony
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Why would you care what an exact meter was in the jungle?
Pick a vine, make up a standard get building. So long as you consistently use the same method of measure you will consistent and make a sound
structure or any thing, it is consistency that is important not the labels.
I often build things with no measuring device at all out in the bush I pick up a stick and that becomes my standard unit of length and go from there.
We crated standard units for communications among our society and to ensure consistency throughout our civilization science, technological and
industrial sections. For them to work every one needs to be taught them and use them, but get rid of society then it is completely arbitrary.
[Edited on 7-4-2018 by XeonTheMGPony]
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Deathunter88
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Here you go: https://en.wikipedia.org/wiki/SI_base_unit
Side note: The kilogram is said to be soon defined absolutely. IE. Not based on a physical object, but rather a concept.
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RawWork
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Well, I feel extreme worry and doubt about units. Can't sleep suspecting they're wrong. Also noticed differences in my sim cards. When I put one sim
card in cell phone it fits perfectly, however another started peeling from both sides, it was too wide. Probably half mm or less. Many products which
claim are same are not same, they make mistakes. In my city all trams stopped working because one rail was moved a little. They fixed it in few hours.
Also seen people dieing in escalators and elevators, probably because somebody missed one nanometer or milimeter. Also many companies withdrawn their
produced cell phones and cars because of one nanometer.
I know that relations are what is most useful and important, e.g. 2:2.
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XeonTheMGPony
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That is what is called "Manufacturing tolerances" Machines will vary due to tempriture and wear, this is unavoidable, the goal is to keep tolerances
as close as possible, higher quality stuff does this more vigorously, cheaper stuff does not.
This is what you are paying for really second to brand name you are paying for the more rigorous checking of the tolerances on the machines and
product, usually a mm is trivial for most things, for machines you get to micrometers.
Even with the most precise machine no two will ever be exactly alike, this is impossible for all intents, but you can have them to a %, for electrical
capacitors 10% of rated value is good, for resisters 1% and 5% are standard tolerances.
Every thing made is designed with this knowledge, a train rail can be out to X amount with no effect on its safety or performance, same as an engine,
and once it starts going out of tolerance it is replaced or repaired.
Deaths on escalators tend to be user error, wearing lose and bagy clothing that can get caught up on the deck, there should be warnings put on as
common sense is dead nowdays.
[Edited on 7-4-2018 by XeonTheMGPony]
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Deathunter88
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That is why things are engineered to have acceptable tolerances, such that a few nanometers or a few millimeters don't cause any detrimental effects.
I think it is incredibly naive to think that escalator/elevator accidents are caused by someone missing a nanometer... And besides, all of this has
nothing to do with the units themselves. How would you know your relation is exactly 2:2 and not 2:2.0000000001?
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RawWork
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I got it now, tolerance + relations is enough. 
Oh, forgot to warn you all, don't be ignorant about 1 nm!!! It can mean 1 kg or 1 tonne. Consider wire that is 1 nm more in diameter. If this wire is
long enough that 1 nm becomes more and more massive the longer it is. After all it's huge difference and can lead to various deaths. Beware!!! 
[Edited on 7-4-2018 by RawWork]
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LearnedAmateur
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Maybe if you’re dealing with many thousands of kilometres, but a nanometre is an incredibly small distance, almost impossible to picture and you’d
be extremely hard pressed to find a safety conscious application which deals with sub-nanometre tolerances. It could matter if we ever get around to
making space elevators for instance if the cable mass has to be extremely tightly controlled, but tolerances would likely be in the tens or hundreds
of nanometres at least, with other safety mechanisms meaning that manufacturing doesn’t require electron microscope tests on every centimetre, for
hundreds of kilometres.
In my line of work, making contact lenses (which obviously need to be very precise) we have a standardised tolerance of 20 micrometres, which goes all
the way from the initial machining run to the hydration. 20 micrometres is equal to 20,000 nanometres and is within the range of the diameter of human
hair - this is enough to ensure perfect vision for a particular prescription. The only safety aspect which is relevant here would be the edges which
would obviously hurt if not polished down, and this just needs a visual inspection using a magnifying screen to make sure it’s rounded down.
Considering the precision here, larger and more mechanical applications like cars and elevators for instance just need larger tolerances - in the
hundreds of micrometres to millimetres depending on how sophisticated it needs to be; basically thousands of times larger than a nanometre which would
be undetectable on these scales. On the other hand, electronics do actually have tolerances in the nanometre range because of how small wires and
transistors are in products like integrated chips and CPUs. However, and especially in safety dependent applications, these are rigorously tested to
ensure they work perfectly before usage so you don’t need to check the dimensions of EVERY component in the sub/assembly.
That brings me to my last point - aside from tolerances, initial safety testing/maintenance is what separates years of flawless operation and
catastrophic failure. Tolerances don’t really matter when technicians keep an eye on equipment that already works, fixing what’s broken. Deaths
usually come about when people skimp on safety, when money is tight so seemingly benign issues are overlooked. This has played a big part in many
airline disasters, where one small component which hasn’t been adequately tested/maintained fails, which has lead to the plane coming apart mid-air
and/or losing control, leading to the deaths of everyone on board. Even things as small as bolts have killed hundreds of people.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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aga
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While the OP is unmeasurably meaningless, this bit of LearnedAmateur's post is intriguing:
Machining the optic material to shape is pretty obvious, but what is the 'hydration' part ?
[Edited on 7-4-2018 by aga]
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LearnedAmateur
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Oh, yeah, the lens plastic (short cylinders called blanks) is hard when on the lathes and then it basically gets soaked for 24 hours, individually in
little vials, to make them soft. The materials are all water absorbent polymers, just referred to as hydrogels, and I believe it’s a dilute solution
of sodium/potassium bicarbonate used.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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aga
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So they are hard enough to machine into shape when 'dry', can then absorb water and remain in substantially the same shape.
That is a seriously good material.
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Fulmen
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As Xeon correctly points out all of the SI-units are arbitrary by nature. If removed from any reliable reference there isn't any way to replicate it,
the best one can do is to find a reliable reference and use that for a new unit. I can't believe I'm saying this, but the imperial system really isn't
that bad to start. While not terribly accurate, the human body is a very practical reference.
We're not banging rocks together here. We know how to put a man back together.
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LearnedAmateur
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Quote: Originally posted by aga  | So they are hard enough to machine into shape when 'dry', can then absorb water and remain in substantially the same shape.
That is a seriously good material.
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That’s pretty much it, the process is separated into ‘dry’ and ‘wet’ manufacturing where I’m in the former cutting the concave surfaces.
All the blanks feel the same as any other plastic really, except for the silicone hydrogel ones which are slightly sticky to the touch. They can hold
between 30% and 90% water by weight, which is nuts for something like 0.5-2mm thick. I have no idea on the chemical composition though, tried to look
up some of the material names used but just get stuff like -filcon, but I believe some are based on polymethacrylate esters and copolymers of such.
Maybe something for another topic?
| Quote: Originally posted by Fulmen | As Xeon correctly points out all of the SI-units are arbitrary by nature. If removed from any reliable reference there isn't any way to replicate it,
the best one can do is to find a reliable reference and use that for a new unit. I can't believe I'm saying this, but the imperial system really isn't
that bad to start. While not terribly accurate, the human body is a very practical reference.
|
As someone who despises Imperial (having been brought up solely on metric), I’d have to begrudgingly agree that in the case of societal dissolution,
it would be a better place to start. Even better though, back to the days of cubits and digits, where the diagram is relevant and could be quite
useful for small scale measurements. Then you’ve got forearms, paces, armspan, and such - to a grown man these all obviously don’t change by much
hence can be employed for rough yet standardised applications.
[Edited on 8-4-2018 by LearnedAmateur]
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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Sulaiman
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There are so many rulers, weights, measuring and reference devices of many types in existence
that even global nuclear war will not change our references.
Although any self-consistent system of measurements could be developed,
if great care is not taken then future school children will have to remember a lot of conversion factors.
CAUTION : Hobby Chemist, not Professional or even Amateur
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XeonTheMGPony
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that's why there are vaults all over the place with full data sets and standards of weight and distance in them, it was thought of! and really we all
should have a small weight standards our selfs for our lab scales.
So lets say a meteor wipes out 90 % of us, the odds are some of the remaining ten will be techs, scientists and such and will have standards on hand,
and the few teachers that will be around will have their old warren but good enough rulers and such.
So any who wish to learn would be able to with the effort to find the knowledge and you'll have the willfully ignorant stumbling around making sh*t up
as they go, so really no different from how things are now!
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LearnedAmateur
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To be fair, we have so many measuring devices in existence that I can’t really imagine we’d have any issues continuing on with our domestic and
scientific measuring capacities. Need a litre of water? Grab a jug from the kitchen. Need to measure out x centimetres/inched/feet? We’ve all got a
plastic ruler or measuring tape tucked away in a drawer. You require y grams/pounds of material? Scales aren’t that uncommon.
More precise measuring tools can be found in factories and other such common buildings if you need to construct something more delicate, and there are
plenty of other types like thermometers and multimeters lying around for most of the remaining population to make use of. Not only won’t you have
the majority ‘stumbling around making shit up’ as you put it, but most of us already use these tools so that eliminates the need to redefine
standardisation in civilisation V2 since we already have the knowledge to continue with.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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RawWork
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But how can you be sure such tools are all synchronized. I had one smartphone that displayed time, and another two that displayed time, and calculator
that displayed time. I still have them. But in one time would eventually (after 1 week from last reset) be 5 minutes forward than in all). While in
calculator it is 10 minutes after all after 2 weeks. Later I realized smartphone had problem with software, when I reinstalled original firmware it
was perfect. While calculator still has problem. Also thermometers and all devices may get too old and start producing wrong data. Sometimes even new
can be produced wrongly.
I am asking you how to be sure that some measurement is right? Can I rebuild these devices from soil and air? Can I compare them to something more
stable and precise? Copying is not stable. The more you copy something, like ruler A to ruler B, ruler B to ruler C, the more difference and errors.
How can humans be sure they did not make mistake?
Is there anything natural stable and standard? Clocks are not. Time is not. I heard 1 second is lost each year. Some will synchronize with that, some
will not. My voltage in home is not 230 V, but 245. Please....
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Deathunter88
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| Quote: Originally posted by RawWork | But how can you be sure such tools are all synchronized. I had one smartphone that displayed time, and another two that displayed time, and calculator
that displayed time. I still have them. But in one time would eventually (after 1 week from last reset) be 5 minutes forward than in all). While in
calculator it is 10 minutes after all after 2 weeks. Later I realized smartphone had problem with software, when I reinstalled original firmware it
was perfect. While calculator still has problem. Also thermometers and all devices may get too old and start producing wrong data. Sometimes even new
can be produced wrongly.
I am asking you how to be sure that some measurement is right? Can I rebuild these devices from soil and air? Can I compare them to something more
stable and precise? Copying is not stable. The more you copy something, like ruler A to ruler B, ruler B to ruler C, the more difference and errors.
How can humans be sure they did not make mistake?
Is there anything natural stable and standard? Clocks are not. Time is not. I heard 1 second is lost each year. Some will synchronize with that, some
will not. My voltage in home is not 230 V, but 245. Please.... |
You seem to have not carefully read the wikipedia link I sent earlier. One second is defined as "the duration of 9192631770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom." That is something that will not change.
Ever.
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LearnedAmateur
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| Quote: Originally posted by RawWork | But how can you be sure such tools are all synchronized. I had one smartphone that displayed time, and another two that displayed time, and calculator
that displayed time. I still have them. But in one time would eventually (after 1 week from last reset) be 5 minutes forward than in all). While in
calculator it is 10 minutes after all after 2 weeks. Later I realized smartphone had problem with software, when I reinstalled original firmware it
was perfect. While calculator still has problem. Also thermometers and all devices may get too old and start producing wrong data. Sometimes even new
can be produced wrongly.
I am asking you how to be sure that some measurement is right? Can I rebuild these devices from soil and air? Can I compare them to something more
stable and precise? Copying is not stable. The more you copy something, like ruler A to ruler B, ruler B to ruler C, the more difference and errors.
How can humans be sure they did not make mistake?
Is there anything natural stable and standard? Clocks are not. Time is not. I heard 1 second is lost each year. Some will synchronize with that, some
will not. My voltage in home is not 230 V, but 245. Please.... |
I was simply referring to measuring devices above all, which will only vary by a small amount, if at all. In a post-apocalypse civilisation,
timekeeping wouldn’t be as stringent as it is today - get up when the sun rises, start to prepare for night when it’s getting dark, a 5-10 minute
difference wouldn’t matter much. If you need to count down to seconds then a stopwatch will do the job fine, it’s not like you need ultimate
precision down to the millisecond. And yeah, over time the data will begin to skew if not calibrated but again, unless ultimate precision is required
(not roughly measuring out metres or grams for instance) it won’t really matter if your electronics produce 0.2V higher than you expected or your
chicken is cooking 5C below what it should be.
Personally, I think it’s a little pendantic to be worrying about measurements that you can’t perform using your hands and readily available tools
in a society no longer dependent upon precision and skill. It’s not like you’re going to be rebuilding a microwave oven from scratch or trying to
make an AR-15 from lumps of iron ore you’ve dug from the Earth. Humanity would start with the basic steps from what is easy to find, and then when
basic principles are established again, then technology will improve once more based on people’s needs.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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Sulaiman
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Rubbish !
Rubbish and abandoned properties with equipment, supplies, instructions etc will be available.
We cannot start again and repeat the technology path as we have taken from the earth all that is easy to take.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Fulmen
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Yes. The speed of light in vacuum is believed to be fixed, in fact both time and distance is defined by it today. There are others as well, like the
elementary charge and electron rest mass. But none of them are available without very advanced technology.
We're not banging rocks together here. We know how to put a man back together.
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aga
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The OP is just a shit post.
Wading in shit is pretty much normal around here these days.
Interesting who posts what, and where.
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Tsjerk
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One gram of water fits in one cubic centimeter and needs one calorie to heat up one degree Celsius
The amount of water contains one mole of hydrogen
One meter you could define as whatever you want, just measure sure everyone uses the same. Same for kilograms.
[Edited on 9-4-2018 by Tsjerk]
I made a quite big mistake on my last sentence
[Edited on 9-4-2018 by Tsjerk]
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Fulmen
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Aga: I don't disagree, if it were up to me both he and a couple of newbies would be tossed out long ago. But at least he managed to ask an interesting
question this time. Now if he could only spend some more time on Wikipedia he might be able to understand the answers...
We're not banging rocks together here. We know how to put a man back together.
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