SI mass unit, why?

[VaPaL]

So, I was thinking, why the unit of mass in the SI is 1000 units (grams). Why what was defined was the KILOgram, not the gram itself? No other unit uses a prefix, they are just the plain unit. Anyone know what is the historical reason (if any) for this. The the base mass was 1000 grams, not just 1 whatever unit?

I know it doesn't change ANYTHING, it's just something that annoys me and got me wondering why.

Edited March 8, 2017 by VaPaL

[Kryten]

The gram was provisionally defined years before the prototypes were built. When they got round to it, they decided it would be very difficult to measure and maintain a 1 gram weight to the required level of precision, so they made it a kilogram.

[VaPaL]

55 minutes ago, Kryten said:

The gram was provisionally defined years before the prototypes were built. When they got round to it, they decided it would be very difficult to measure and maintain a 1 gram weight to the required level of precision, so they made it a kilogram.

Thought that might be something like that, but didn't know that the gram came earlier. For me, it was something like the meter, someone take a of some length of wood and said that for that time on, that would be 1 meter (loose and jokingly speaking). So for mass, someone take a bunch of some material and said that it was equal to 1 kilogram (instead of gram).

Well, good to know, thanks!

[Gaarst]

The gram was defined as the mass of a cubic centimetre of water.
The SI unit of mass was defined as the mass of 1 litre of water which turned out to be 1 kg (or 1000 g), so instead of creating a new unit, they kept the kilogram.

Edited March 9, 2017 by Gaarst

[mikegarrison]

43 minutes ago, VaPaL said:

Thought that might be something like that, but didn't know that the gram came earlier. For me, it was something like the meter, someone take a of some length of wood and said that for that time on, that would be 1 meter (loose and jokingly speaking). So for mass, someone take a bunch of some material and said that it was equal to 1 kilogram (instead of gram).

Well, good to know, thanks!

That's not where the meter came from. It was defined as 1/10000000 of the arc distance from the equator to the north pole.

[VaPaL]

1 hour ago, mikegarrison said:

That's not where the meter came from. It was defined as 1/10000000 of the arc distance from the equator to the north pole.

Yep, I knew only from the bar forward, never heard about anything ealier than that! Very cool!

[kerbiloid]

2 hours ago, mikegarrison said:

It was defined as 1/10000000 of the arc distance from the equator to the north pole.

1/40000000

4 hours ago, VaPaL said:

Why what was defined was the KILOgram, not the gram itself?

Because when it was gram (Centimeter-Gram-Second system), the water cube was in centi-meters.

XVIII cent. Gram is invented, its etalon - 1 l ow water, weigthing 1000 g = 1 kg.
1889 The current etalon of kg is created instead of water glass.
XX cent. Kilogram is officially used as the unit because kilograms are used more often than grams IRL.

 

[mikegarrison]

8 minutes ago, kerbiloid said:

1/40000000

No. 1/10000000 of the distance from the equator to the north pole. Just like I said.

You must be thinking it was 1/40000000 of the circumference of the Earth, but it was not that.

It's easy enough to look this up, if you doubt me.

In fact, there was an argument between Thomas Jefferson and the French Academy about exactly which longitude should be used to make this measurement. The French won the argument. They measured between Barcelona and Dunkirk (which just happens to go right through Paris, which is why the French thought that of course this was the best longitude to immortalize as the official meter). Then since they knew the latitudes of their end points, they extrapolated their measurement and got the distance of the full arc from equator to pole.

But they messed up the measurement! And the guy who did it (Pierre-François-André Méchain) knew he messed up the measurement, but the error had occurred near the start of the line, in Spain. And France was now at war with Spain, so he couldn't go back and fix it. It's a very interesting story.

There is at least one book about this. The one I read is called The Measure Of All Things, by Ken Adler.

[cantab]

The metre, gram, and second were all developed somewhat independently, with no real intention of tying them together into a system of physical units. That came later, and in fact *several* systems were used. There was CGS - centimetre, gram, second - which itself spawned numerous variants when it came to working with the new science of electromagnetism. There was MKS - metre, kilogram, second - with electromagnetic units considered easier to work with. There was MTS - metre, tonne, second. There were 'gravitational units' using kilograms-force as the force unit and deriving the mass unit.

In the event the MKS system 'won' and gave rise to SI. Of note is that the MKS system defines an electrical base unit, the ampere. Doing that actually avoids some oddities of CGS units.

There was a metre-gram force-second system, but I don't believe there was ever a metre-gram (mass)-second system. I'm not sure why, maybe it just wasn't regarded as useful.

On a final note, the original metric units were the grave, the mass of a litre of water, and the gravet, 1/1000 a grave. But this was the French Revolution, and 'grave' was also an aristocratic title and to use that word for a weight was unacceptable! The gravet was renamed the gramme (from Latin gramma, small weight) and the grave became the kilogramme. So basically, the SI base unit of mass is the kilogram because of politics.

[YNM]

Basically what cantab said - it boils down to the french. After all, neither britons nor germans have anything to do with SI at first (more so the rest of the world). It's also why CIPM and BIPM is in France. Metre Convention and CGPM is (was) also held in france. Interesting read those things are, how something that's now adopted as an international standard arose from a national revolution in europe...

I thought this was about the reference kilogram, which is problematic.

Edited March 9, 2017 by YNM

[mikegarrison]

9 minutes ago, YNM said:

Basically what cantab said - it boils down to the french. After all, neither britons nor germans have anything to do with SI at first (more so the rest of the world). It's also why CIPM and BIPM is in France. Metre Convention and CGPM is (was) also held in france. Interesting read those things are, how something that's now adopted as an international standard arose from a national revolution in europe...

I thought this was about the reference kilogram, which is problematic.

Yes.

The book I referenced up above had a pretty good chapter or two explaining the background of the whole situation. It was tied into Enlightenment humanistic principles, a political desire to get rid of any remnants of the Ancien Régime, and an economic need for the standardization of measurement units.

[kerbiloid]

2 hours ago, mikegarrison said:

No. 1/10000000 of the distance from the equator to the north pole. Just like I said.

You must be thinking it was 1/40000000 of the circumference of the Earth, but it was not that.

It's easy enough to look this up, if you doubt me.

My inattention about "circumference" vs "equator to pole", just as I had read, originally it was "1/40000000 of Paris meridian circumference".
As a meridian has 4 quarters, this definition means almost what you said, but an average of all four "equator to pole" quadrant lengths, so was more accurate.

[Nibb31]

The French Revolution also tried to adopt a metric calendar (12 months, 30 days, 10 days in a week, plus 5 or 6 extra days to catch up), but it was abolished after Napoleon in 1806. They even tried a metric 10-hour day, but that didn't work.

[mikegarrison]

37 minutes ago, kerbiloid said:

My inattention about "circumference" vs "equator to pole", just as I had read, originally it was "1/40000000 of Paris meridian circumference".
As a meridian has 4 quarters, this definition means almost what you said, but an average of all four "equator to pole" quadrant lengths, so was more accurate.

Except no, it was less accurate about what actually historically happened.

9 minutes ago, Nibb31 said:

The French Revolution also tried to adopt a metric calendar (12 months, 30 days, 10 days in a week, plus 5 or 6 extra days to catch up), but it was abolished after Napoleon in 1806. They even tried a metric 10-hour day, but that didn't work.

Interestingly enough, the rest of the metric system was also abolished under Napoleon. Even though it was the French who had measured the meter, they abandoned it. However, other countries took it up and the French later returned to it.

Also interesting was that the American Thomas Jefferson was a major proponent of establishing the metric system, but almost 250 years later the US is one of the only countries in the world that does not use it as the typical system of measures.

[DerekL1963]

19 minutes ago, mikegarrison said:

Also interesting was that the American Thomas Jefferson was a major proponent of establishing the metric system, but almost 250 years later the US is one of the only countries in the world that does not use it as the typical system of measures.

Basically because the ship carrying the metric prototypes sank.

[mikegarrison]

11 minutes ago, DerekL1963 said:

Basically because the ship carrying the metric prototypes sank.

I've read that it was part of a compromise. Jefferson wanted decimal money and measures. Hamilton wanted traditional money and measures. Washington agreed to decimal money and traditional measures.

[DerekL1963]

31 minutes ago, mikegarrison said:

I've read that it was part of a compromise. Jefferson wanted decimal money and measures. Hamilton wanted traditional money and measures. Washington agreed to decimal money and traditional measures.

All three were long deceased by the time an official standard system was adopted in 1832.

[p1t1o]

Ugh, I hate reading about how messy and made up our lovely system of units really is...

[YNM]

1 hour ago, p1t1o said:

Ugh, I hate reading about how messy and made up our lovely system of units really is...

It's because they're history, the paths that human mind traced long ago. Shows really how messy our thoughts are.

[p1t1o]

3 minutes ago, YNM said:

It's because they're history, the paths that human mind traced long ago. Shows really how messy our thoughts are.

Stupid biological nature...

[YNM]

But if it wasn't that way some parts of it probably won't be more interesting than the others

[kerbiloid]

They should implement a new system, based on Planck units. But it's still delayed.

This would be the first system where the units have solid background.

From the other hand, then we'll need more prefixes.
Because for a daily human use there are: terayottaplanck (16 m) and gigayottaplanck (1.6 cm).
1 zettayottaplank = 54 seconds.
But 22 grams = 1 megaplanck. Mass is fine with it.

[monstah]

52 minutes ago, kerbiloid said:

They should implement a new system, based on Planck units. But it's still delayed.

This would be the first system where the units have solid background.

From the other hand, then we'll need more prefixes.
Because for a daily human use there are: terayottaplanck (16 m) and gigayottaplanck (1.6 cm).
1 zettayottaplank = 54 seconds.
But 22 grams = 1 megaplanck. Mass is fine with it.

 

1 KWh ~ 1.8 milliplanck. Doable, too  

[VaPaL]

2 hours ago, YNM said:

messy our thoughts are

 

2 hours ago, p1t1o said:

biological nature

I don't think it's because they are messy, nor blame our biological nature. Measurements are just a way to reference something, A fits this amount of times inside B (or weight this amount more than). This need was fulfilled with what people had and knew at a specific time, as time passes, knowladge increases and need to a better and unified system arises, the units change. If we make everything planck based as @kerbiloid suggests, who knows, maybe 100 years from now it will be as stupid, arbitrary and made up as the one we uses now.

[p1t1o]

4 minutes ago, VaPaL said:

...who knows, maybe 100 years from now it will be as stupid, arbitrary and made up as the one we uses now.

This is the messy part, I want perfect understanding NOW!