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Imperial versus metric


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What is even more suspicious is how close 1 imperial foot is to 1 light nanosecond.

It does make it really easy to guesstimate astronomical distances in conversation.

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On 7/4/2021 at 11:16 PM, Beccab said:

People still use imperial != imperial is necessary

That may be true from some very abstract philosophical point of view. Like wars could be ended if no-one would kill or poverty could be ended if wealthy people would always help poor. But practically that is very false. If you are worker you use units your boss order to use. If you are boss or company owner you use units customers want to. If you are politician you know that any law can not overcome conservative attitude and traditions. Eventually you can not find an individual in real world who can avoid imperial and other strange units without significant trade offs in practical life.

Situation is not perfect in countries or scientific community which use SI-system. There are many historical special units in most areas which stay alive during decades. For example ångströms (1 Å =100 pm) and 1/cm as unit of energy in spectroscopy.

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45 minutes ago, Hannu2 said:

Situation is not perfect in countries or scientific community which use SI-system. There are many historical special units in most areas which stay alive during decades. For example ångströms (1 Å =100 pm) and 1/cm as unit of energy in spectroscopy.

Fortunately, the ones that do survive tend to be the ones most compatible with the SI units, though. I mean, the liter is not a SI unit, but it's so easy to convert back and forth it might as well be because it's a multiple of 10 SI units. The same with the examples you mention, they work mostly as a shorthand for common multiples of 10 of other SI units. 

The whole reason why Imperial is such a royal pain to work with is that it's not linear like that. You've got fifty-seven Godfreys to a Worthington, which itself is two-fifths of a Lengthwise Flagpole and defined using the time it takes an unladen swallow to cross the shadow of a priest at noon on St. Longfellow's Day. 

Okay, maybe not quite, but there are Imperial units like a fathom (2.02666... yards), a perch (272 1/4 square feet, or 30 1/4 square yards), a fluid ounce (1.73339 cubic inches), or a hundredweight (112 pounds). These units do not scale nicely at all with each other.  They are little used for precisely this reason, though, which I believe to be the case with most near-metric units that don't scale well either. But the easy ones have a certain right to life, when they fit so nicely in with the rest.

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Not to mention the confusion that arises when there are two competing imperial units, such as the gallon (3.785 litres) and the other gallon (4.546 litres), which are both imperial measurements but only one of them is referred to as the imperial gallon. 

Then you have the ton, which is either 1016 kg or 907 kg depending on which standard you are following, 

There is also the ounce, which is, of course, 28 ml. Or 30 ml. 

...and many more. 

 

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5 hours ago, Deddly said:

Not to mention the confusion that arises when there are two competing imperial units, such as the gallon (3.785 litres) and the other gallon (4.546 litres), which are both imperial measurements but only one of them is referred to as the imperial gallon. 

Then you have the ton, which is either 1016 kg or 907 kg depending on which standard you are following, 

There is also the ounce, which is, of course, 28 ml. Or 30 ml. 

...and many more. 

 

One of my favourites is the quarter, which may be a unit of length, volume, or weight, depending on context. Of course, the quantities described by each definition of a quarter has no relation to each other either. It's either 22.9 centimeters, 12.7 kg, or 242 liters. 

In other words, I would rather not order spaghetti by the quarters.

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As a machinist, it doesn't matter.  Everything I do is in decimal [unit].   I do decimal inches or millimeters.   If I'm making something 25.4mm or 1.000",  the math is all the same either way.  It's decimal.   My base unit is either tenths of a mil or thousandths of an inch.   So if I "take this part up 2", it's increasing it .2mm or .002", it just depends on where the customer is located.   99.9% of my work is in decimal inches though, just makes things uniform.   But we only talk in the single unit, there's no conversions beyond that base unit.   If our raw stock is 20ft long, we usually don't say 20ft, we say 240 inch, and I'll be able to cut 12 20 inch blanks from that raw bar.   Never 1 foot 8 inch.   20 inch.   Single decimal unit. 

As a woodworker, fractional imperial is by far superior.    Wood moves.   It changes dimensions with humidity and temperature.   A fractional measurement implies that I understand that 1/32 of an inch is not going to be the same 1/32 of an inch in a few months.  If I'm ordering 1/2" ply, I know there will be some variation to it.   But 12.7mm ply just seems like it should be exactly 12.7mm thick... but it's not... there's quite a bit of variance.   So for woodworking, a measurement system that has some fudge built into it is a superior system.

As a 3d printer....  Well, it depends on what I'm designing and for what.   If it's a truly original design that isn't rigidly constrained by any outside item, then I usually go with metric.  But if a design is to interface with another object, I'll use the system that other object was designed around, or for the hardware I intend to use with it.   1/4"-20  vs 6mm-20 bolts?  Really no difference in application, I'll just stick with that system.   My battery pack I'm designing is 2"x6" with 1/2" radii corners?  Then imperial it is.   But as with being a machinist, I work with decimal, not fractional units. 

As an armchair scientist, metric is far preferred for all the arguments given above. 

But as a Human... especially with temperature...  Fahrenheit is the superior system.   Yes it makes absolutely no sense when compared to Centigrade and the properties of water.... but if you're talking about the properties of Humans....  The acceptable ranges for Humans to "comfortably" exist is 0f-100f.     Anything above or below that, and you should consider taking extreme measures to survive safely.    Of course, some will argue that 100f isn't that hot, and others will say that 0f isn't that cold, but on an average... it seems to fit human experience better than -20c - 40c.

I could make an argument that imperial feet is better for human height... but that's probably just due to what I know.   Under 5' is really short, mid 5' is average, under 6' is still short, and over 6' is tall (being 6'3", I might be biased a bit).    But similar concepts could be applied to 10cm blocks, so honestly the argument is moot. 

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6 hours ago, Gargamel said:

As an armchair scientist, metric is far preferred for all the arguments given above. 

Thats what it seems to be by far. I am a mechanic by trade and the conversion to metric was a long and messy one, so I have learned to use most measurements interchangeably. I also see the imperial system as a system that gives you some leeway, where I see the metric system as much more exacting.

 

Now, I am in the USA (obviously) but if you see enough of my posts, I convert to metric for sake of our non US members. I also usually try to state what monetary system I am using when mentioning a price as well. For myself its no hassle to convert and helps to reach a larger audience.

 

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About the time.

In KSP there should be either six hours divided in quarters, or 24 hours per day.

Because the KSP models are usually 24-angled.

So, the cloc dial should have 24 ticks.

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On 7/10/2021 at 3:09 AM, Gargamel said:

But as a Human... especially with temperature...  Fahrenheit is the superior system.   Yes it makes absolutely no sense when compared to Centigrade and the properties of water.... but if you're talking about the properties of Humans....  The acceptable ranges for Humans to "comfortably" exist is 0f-100f.     Anything above or below that, and you should consider taking extreme measures to survive safely.    Of course, some will argue that 100f isn't that hot, and others will say that 0f isn't that cold, but on an average... it seems to fit human experience better than -20c - 40c.

The counter-argument to this is that having a clear delineation around the freezing point of water plays a much more important role in identifying hazardous weather conditions in our day to day lives.

32f is rather arbitrary given the major effects freezing water has on our eco-system.

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On 7/10/2021 at 1:09 PM, Gargamel said:

But as a Human... especially with temperature...  Fahrenheit is the superior system.   Yes it makes absolutely no sense when compared to Centigrade and the properties of water.... but if you're talking about the properties of Humans....  The acceptable ranges for Humans to "comfortably" exist is 0f-100f.     Anything above or below that, and you should consider taking extreme measures to survive safely

***

A natural human-based temperature scale is required.

Low boundary = when the liquiding gets frozen in midair.
High boundary = when it boils in midair.

***

As the youtube videos show, a pure water freezes in midair at ~ -45°C.

But the liquid is a solution of salts, like seawater is.
The Mythbusters tried this, and it wasn't frozen at -57°C.

As normally the liquid freezes at -5°C, probably, we can take -60°C as the low boundary.

***

The high boundary seems to be +100°C.

But no, it's the temperature of the liquid itself to boil.
But in a bath they splash water on the stones, and it boils once it touches the stones,
The stones are are at least +150°C hot, but optimally+300°C and more . While the air temperature is ~60..70°C, up to 110°C and a little more.

As we need a clear indicator, the stones temperature is more relevant than the temperature of air. We can estimate it by color.

***

But after having steam in a bath, they traditionally run out and jump into the ice hole to cool.

Spoiler

zakalivanie-posle-bani.jpg

***

From hence we get the natural human bath temperature scale.

Low boundary ~=-60°C, when it rips off by freezing.
High boundary ~=+150°C, when it rips off by boiling.

Edited by kerbiloid
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On 7/10/2021 at 6:09 AM, Gargamel said:

As a machinist, it doesn't matter.  Everything I do is in decimal [unit].   I do decimal inches or millimeters.   If I'm making something 25.4mm or 1.000",  the math is all the same either way.  It's decimal.   My base unit is either tenths of a mil or thousandths of an inch.   So if I "take this part up 2", it's increasing it .2mm or .002", it just depends on where the customer is located.   99.9% of my work is in decimal inches though, just makes things uniform.   But we only talk in the single unit, there's no conversions beyond that base unit.   If our raw stock is 20ft long, we usually don't say 20ft, we say 240 inch, and I'll be able to cut 12 20 inch blanks from that raw bar.   Never 1 foot 8 inch.   20 inch.   Single decimal unit. 

There was a Scott Manley video where he was talking with his brother.  His brother does (or did however long ago it was published) a lot of producing thin films.  He kept talking about "mils" and I was never sure if he meant milimeters or dealt enough with the American market to be talking about US "mils" which are mili-inches.  I'm pretty sure he meant mm.

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I saw a meme today that reminded me of this real issue. It's not that there are 12 inches in a foot instead of 10, etc.

The real issue that causes problems is that:

  • pounds => Newtons
  • slugs => kilograms

Pounds are force (unless they aren't, and thus "lbm"), while kg are mass. Which means if you weigh yourself on the scale and you weigh 200 lb, that's actually correct, but if you "weigh 100 kg" it's wrong. You actually weigh about 980 Newtons, but on Earth that implies your mass is 100 kg.

Anyway, the problem is that the old system is force-based, but SI is mass-based. And that tends to mean you have to remember to factor "g" into your conversions.

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2 hours ago, mikegarrison said:

Pounds are force (unless they aren't, and thus "lbm"), while kg are mass. Which means if you weigh yourself on the scale and you weigh 200 lb, that's actually correct, but if you "weigh 100 kg" it's wrong. You actually weigh about 980 Newtons, but on Earth that implies your mass is 100 kg.

Extremely silly point. If you use a spring scale, you're ackshually 980 Newtons, but if you use a balance scale, you're ackshaully 100 kg?

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3 hours ago, mikegarrison said:

I saw a meme today that reminded me of this real issue. It's not that there are 12 inches in a foot instead of 10, etc.

The real issue that causes problems is that:

  • pounds => Newtons
  • slugs => kilograms

Pounds are force (unless they aren't, and thus "lbm"), while kg are mass. Which means if you weigh yourself on the scale and you weigh 200 lb, that's actually correct, but if you "weigh 100 kg" it's wrong. You actually weigh about 980 Newtons, but on Earth that implies your mass is 100 kg.

Anyway, the problem is that the old system is force-based, but SI is mass-based. And that tends to mean you have to remember to factor "g" into your conversions.

Once human space travel between places is occurring regularly, the correct terminology will be “how much do you mass?” (a very important measure for space travel, probably not left to the honour system)

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I believe metric is superior in all cases, though I do have a soft spot for imperial with regards to temperature:

0-100 in Fahrenheit is a good scale of the temperatures humanity usually experiences, with 0 being very cold but survivable, and 100 being very hot but survivable.

Meanwhile with Celsius, 0 is mildly chilly, while 100 is far beyond anything humanity experiences.

Also, water boils at different temperatures depending on altitude, so Celsius' main advantage of being based on water's boiling temperature is negated for a lot of the world, making it just as arbitrary as Fahrenheit.

Edited by coyotesfrontier
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2 hours ago, NFUN said:

Extremely silly point. If you use a spring scale, you're ackshually 980 Newtons, but if you use a balance scale, you're ackshaully 100 kg?

What does a balance scale have to do with anything?

Weight is a force. Mass is mass.

As an engineer, it's tricky that the basic equations we use all the time (like F=MA) don't just replace lb for kg or vice versa in the same spot, but actually have to put lb in for F but kg in for M.

Even stuff like whether an airplane has a maximum certified takeoff weight (in lb) or a maximum certified takeoff mass (in kg) can lead to issues.

The fundamental relationship of steady-state cruising flight is that Lift=Weight and Thrust=Drag. Those are all forces, so they can be expressed in pounds or in Newtons. But not in kilograms, although most people relate pounds and kilograms as being equivalents to each other. 2.2046 -- I use that all the time to convert pounds and kilograms, but I always have to be careful because one is actually a force and the other is actually a mass.

I'm not saying one is better than the other, but I usually prefer working in SI units because mass tends to be a better base unit than force for a lot of things. Powers of 10 are trivial compared to the real issue of whether your customary base units are mass or force.

Edited by mikegarrison
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5 hours ago, mikegarrison said:

Pounds are force (unless they aren't, and thus "lbm"), while kg are mass. Which means if you weigh yourself on the scale and you weigh 200 lb, that's actually correct, but if you "weigh 100 kg" it's wrong.

"kilogram-force" and "tonne-force" aka кгс & тс were absolutely widely used in Russian before being replaced in 1970s with SI, and are still in use outside of science.

52 minutes ago, mikegarrison said:

Weight is a force. Mass is mass.

The Earth shops and markets are placed in a place with ~9.81 m/s2 gravity.

Scientisifc and technical application operate with masses and forces, and almost never with "weight". 
The "weight" is an archaic value, used only as an illiterate substitution for "mass" at a market, or for "the force pressing the pad" in other cases.

Anyway it's almost never used in the high wisdom.

52 minutes ago, mikegarrison said:

Even stuff like whether an airplane has a maximum certified takeoff weight (in lb) or a maximum certified takeoff mass (in kg) can lead to issues.

The English-speaking engineers should do something to these obsolete abstractions.

Because it never causes issues if use the accurate terminology rejecting the historical stuff. In SI and correct terminology it's absolutely exact.

The "weight" can make sense when you calculate tarmac layer for the plane parking, and only just because it hasn't changed a lot since early XX when the tables were calculated, and nobody cares to replace them.

In all other cases the "weight" is a colloquial substituon for "mass" and its usage is strongly discouraged as illiteracy.

Edited by kerbiloid
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On 7/20/2021 at 10:02 PM, mikegarrison said:

What does a balance scale have to do with anything?

With a spring scale, you're measuring the weight of the object by balancing the force exerted by the springs vs the force exerted by the mass. Given a different local acceleration, the spring scale would register a different rate. Given an appropriate gradient, the balance scale should always give the right answer--you're comparing masses directly with each other, and although the medium is via their apparent weight, in a very real sense the result you're getting is the object's mass.

 

In other words, with a spring scale, given what you're measuring and what you're measuring it with (the object and the parameters of the spring), you can calculate the local force field. With a balance scale, you know nothing about the local environment other than there's some persistent direction of force.

 

Anyway, in real terms, so long as the system is self-consistent in which value it prefers, neither is inherently preferable; one might be useful for some use-cases over others, but that line of attack is like debating between mks and cgs units, which is not an argument any sane person wants to have. The idea that imperial being bad because it's hard to convert to an entirely different system assumes that the different system is better anyway, and that when doing your own calculations, you would always want to convert

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I understand how balance scales work, but IMO you are so very missing the point.

I suppose I should clarify that part of the problem is simply that legally a pound actually is mass. But "pound" is also used as the word for the force when a pound of mass is accelerated at one standard gravity. And usually people don't specify that they mean pound-force (lbf) -- they just say "pound" (lb). Using the same word for a force and a mass is extremely confusing, especially since it is actually more often used as a force but is legally defined as a mass. 

Edited by mikegarrison
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On 7/10/2021 at 5:09 PM, Gargamel said:

The acceptable ranges for Humans to "comfortably" exist is 0f-100f.

idk, to me the only acceptable temp range is 59-86 deg F (15-30 deg C), with body temp obvs in the spread of 95-99 deg F (35-37 deg C). In this case if anything celcius makes a bit more sense esp. regarding room temps.

Then again I live in the tropics where it's hot all the time.

SI units however uses kelvins, not celcius.

On 7/21/2021 at 9:51 AM, kerbiloid said:

The Earth shops and markets are placed in a place with ~9.81 m/s2 gravity.

Scientisifc and technical application operate with masses and forces, and almost never with "weight". 

... with the exception of building mass vs. force. We use kgf (and tonnes-force) often enough in buildings, it's really easy to forget that we're really dealing with weight (therefore forces) and not mass, esp. when you have to convert that into actual mass for analysis (ie. in dynamic analysis or approximations of it).

Edited by YNM
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6 hours ago, mikegarrison said:

legally a pound actually is mass.

Oh.  I suppose you mean In the United States.   I went to school in the US and they taught me 'slug' for the unit of mass.  Do you not use that anymore?

So the term 'pound'  or 'lb' for the unit of mass (454 g)   and the term 'lbf' for the unit of force (4.45 N) is it?

Edit: But that can't be right, because then Newtons' law F = m a would have to be F = m a / g

Reading again above I see:

On 7/21/2021 at 3:02 AM, mikegarrison said:

but I always have to be careful because one [pound] is actually a force and the other [kilogram] is actually a mass.

So I gather that in engineering people use most often 'pound' for 'lbf',  and need only be wary that sometimes people use 'pound' according to the legal definition to constrain a mass.   And  I suppose the distinction rarely makes a physical difference on Earth; maximum takeoff mass is always applied in locations with 9.8m/s² gravity.

Edited by OHara
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Newton used pound because he was not aware of Newton.

Watt use horse powers because he was not aware of Watt.

Others, too.

The metric units are named after the people who even didn't know about them and were using Imperial units.

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3 hours ago, OHara said:

Oh.  I suppose you mean In the United States.   I went to school in the US and they taught me 'slug' for the unit of mass.  Do you not use that anymore?

In my experience, no one uses slugs. But maybe there are some engineering disciplines where they get used all the time. I wouldn't know, because I've been in my little airplane world my entire career.

I do know, from discussions with my dad (a civil engineer), that different disciplines use different things.

Edited by mikegarrison
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