http://www.newscientist.com/article.ns?id=dn7208

World’s most sensitive scales weigh a zeptogram
2005-03-30 14:45
NewScientist.com news service
Celeste Biever

Click on the above link to read this fascinating article


This article says it all. If there is anyone ever looking for a definitive reason why metric is far superior to imperial it is in the fact that metirc is versatile throughout the entire spectrum of measurement.

With metric, you can measure efficiently, consistantly, coherantly and accurately from the universe of the atom to the far depths of outer space. There is nothing the metric system can not handle.

It can have a go at driving my mini.

Bet it can't drive it as fast as I can.

re (Eric O'Brain): "There is nothing the metric system can not handle"


REPLY: Dear Mr O'Brain, tell me one thing that metric can handle that Imperial can't

How about electric current?

That's like me saying BHP cannot be metric!

(think about it)

Electric current

hmmm

The impere:

The impere is that constant current which, if maintained in two straight parallel conductors of negligible circular cross-section and placed 1 yard apart will produce a force of 2 smidgins per mile of length.

Oh dear I've run out of light bulbs.

I wonder if they've got any one eighth horsepower light bulbs down the shop today? I'll go and ask.

I like smidgins

Actually Stan, Horsepower is used for mechanical stuff, not electronics.


P.S. I like your Impere, Idea, but replace the units with inches, feet and pounds and we might be getting somewhere.

<<
Actually Stan, Horsepower is used for mechanical stuff, not electronics
>>

... and (kilo)watts are used with mechanical and electrical systems while joules (1 watt is 1 joule per second) is used with amongst others, electrical, mechanical, geophysical and chemical systems.

Indeed. And?

re: "REPLY: Dear Mr O'Brain, tell me one thing that metric can handle that Imperial can't"

REPLY: Just thought I'd ask that one again

"""REPLY: Dear Mr O'Brain, tell me one thing that metric can handle that Imperial can't"""



Electricity for one! There is no imperial equivalent to volt, ohm, ampere, coulomb, hertz, farad, henry.

Magnetism - There is no imperial equivalent to weber or tesla.

Nuclear Energy - There is no imperial equivalent to bequerel, grey, sievert.

Illumination - There is no imperial equivalent to the lumen and the lux.

Chemistry - There is no equivalent to the katal or the mole.

There are more that can be seen here:

http://www.unc.edu/~rowlett/units/siderive.html


There are no small units in imperial to match the metric prefixes from micro and below. Example, there is no way to equate the prefixed unit zeptogram in imperial.

Does this answer your question?

"""P.S. I like your Impere, Idea, but replace the units with inches, feet and pounds and we might be getting somewhere. """"


Yes, laughed at for being ignorant.

"""That's like me saying BHP cannot be metric!"""

It can be metric, but not SI. The watt is the only legal SI unit. See: http://www.bipm.fr/en/si/

The old metric but not SI unit of horsepower (PS and CV) were defined as the power needed to raise a 75 kg mass one metre in one second. There was no "B" associated with this "HP". It is now obsolete as are all non-SI old metric and imperial units.

Anything that was formerly designed in any of the various horsepower units is now done using the watt. If the horsepower is still seen, it is just an afterthought or conversion from the true SI unit.

Actually, there are imperial equivalents to many of these electric and engineering units.
For example, the "mole" is actually short for "gram-mole". You can just as easily use pound-moles, kilogram-moles, or a mole based on any other unit of mass, and engineers in the United States do. From this, you can have any type of katal, for example, lb-mol/s.
For other units, they have been adapted into SI but are not necessarily metric. For example, the hertz is simply the reciprocal second. Seconds are just as much imperial as they are metric. Same goes for the becquerel.

<<<REPLY: Dear Mr O'Brain, tell me one thing that metric can handle that Imperial can't >>>

I think its more a case of metric handling things better, rather than handling things that imperial can't.

You can measure anything in any unit you want. The advantage of metric units is that they relate to each other in a logical and consistent way, and are universally recognised and understood.

My mini is - supposedly - over 100 BHP.

One needs a rolling road to check this though.

"""Actually, there are imperial equivalents to many of these electric and engineering units.
For example, the "mole" is actually short for "gram-mole". You can just as easily use pound-moles, kilogram-moles, or a mole based on any other unit of mass, and engineers in the United States do. From this, you can have any type of katal, for example, lb-mol/s."""

Incorrect! The mole is specifically defined as (from rowlett):

"The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12.

When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles."

If you base the mole on any other mass unit, then it isn't a mole. It is something else. The only unit defining "amount of substance" is the metric unit mole.


"""For other units, they have been adapted into SI but are not necessarily metric. For example, the hertz is simply the reciprocal second. Seconds are just as much imperial as they are metric. Same goes for the becquerel."""

Incorrect! The second is an SI base unit. The hertz and becqerel are SI derived units from the second. They and many others are used even when imperial is used because there are no specific equivalents in imperial. Imperial can create a set of units of its own for any quantity, but at this point in time nose do exist and none never will. Thus the SI units must be used.

<<
The old metric but not SI unit of horsepower (PS and CV)
>>

P andd S and C and V are actually the first letters of the German and French words for "horse" and "power".

Thanks for breathing some accuracy and truth into his stuff, Martin!

"If you base the mole on any other mass unit, then it isn't a mole. It is something else. The only unit defining "amount of substance" is the metric unit mole."

LOL!
This from the bloke who translated my "how a record is made" into metric!!!

So using your limited mentality a 12" records cannot be measured in metric. Or if you do then it ceases to be a record!!!!




He gets better by the day!

ENB: "Incorrect!"

My proposed impere was a joke of course (but it was fun and I enjoyed making it up)

It did make a subtle point though. Take a look at the SI definition of the ampere:

"The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 x 10^–7 newton per metre of length."

Notice how small the force is between the wires, 200 nN (200 billionths of a newton). That was the reason for "smidgin" which was actually an old imperial unit of mass (from which infer force of gravity like the pound-force). Quite small but still not small enough so to make up for it had to be "per mile". The idea was to get the impere to be comparable in size to ampere.

So if you wan't imperial versions of electromagetic units you have to invent something to handle very small quantities.

Which brings me to the obvious question. If traditional or customary units are deliberately non-decimal (coz they like 12 etc) what do you do about masses of the order of micrograms, like you get in farmek, er, pharmecoo, (oh sod it!) drug doses?

You could invent a new unit and give a name but what then do you do about the next few orders of magnitude down? Back to square one. In metric they go right down to 10^-24 (yocto) or just use the decimal system (the prefixes are optional).

In the end we are lead to the obvious conclusion that unless a system of measurement is decimal it will always be limited in its range of application. You could decimalise imperial units sure (e.g. nano-ounce) but you just end up with a bastardised version of metric, so you might as well use the proper thing in the first place!

The pound-mole is a perfectly legitimate unit. Erin, I don't care what the regulations say, I care about what is used in practice. Anyone else want to comment on this?

And the second was not originally an SI unit. It is much older than the SI. In fact, it was used as part of the English system of measurements before SI even existed.

Bud wrote

<<
And the second was not originally an SI unit. It is much older than the SI. In fact, it was used as part of the English system of measurements before SI even existed.
>>

If you are being pedandic, it is worth noting the following extract from the BIPM site (www.bipm.org/en/si):

<<
The 11th General Conference on Weights and Measures (1960) adopted the name Système International d'Unités (International System of Units, international abbreviation SI), for the recommended practical system of units of measurement.
>>

This means that most SI units predate the name "SI".

"""The pound-mole is a perfectly legitimate unit. Erin, I don't care what the regulations say, I care about what is used in practice. Anyone else want to comment on this?"""


It may be, but it not used. Rowlett defines the "pound-mole" as being:

pound mole (lbmol)
a unit of amount of substance. One pound mole of a chemical compound is the same number of pounds as the molecular weight of a molecule of that compound measured in atomic mass units. Thus the pound mole is equal to exactly 453.592 37 moles.

In other words, it is an SI mole scaled by the conversion factor of the gram to the pound. Thus in essence it is a clone of the SI unit mole. A true imperial unit for amount of substance would be defined from some basic chemecal element, not from an existing SI unit.

Units like pound-mole may have been contribed at a time when imperial was more used in Englsih speaking country physics and chemical laboratories. But since imperial has been phased out of such places and SI is the defacto standard, the existance of a pound-mole is zero if it ever did exist beyond the possibility. Maybe if there was an imperial equivalent to the BIPM, there might be imperial versions of some of the SI units. But the greater problem would be in adoption. No one would adopt it! The existance of the BIPM assures the demise of imperial and its USC sister.



"""And the second was not originally an SI unit. It is much older than the SI. In fact, it was used as part of the English system of measurements before SI even existed."""

SI formalised already existing units into a coherent and consistent family of units. At that time the some of units were defined more precisely., The present definition of the second was adopted in 1967 (http://www1.bipm.org/en/si/si_brochure/chapter2/2-1/2-1-1/second.html). The second may predate SI, but SI defined it precisely to what it is today. The second is not the first choice of a time unit used in imperial. The minute is more used in imperial then the second.

"""So using your limited mentality a 12" records cannot be measured in metric. Or if you do then it ceases to be a record!!!!""""


But it has been done and proven that records are in fact either 300 mm or 302 mm, but not 305 mm? Are you trying to tell us that the inch has been redefined again? If you are going to insist on stating 12 inch records, you must then add a clarifier to denote its true size. For example: 12 inch (302 mm) or 12 inch (300 mm). Otherwise we are not sure which of the two standards you are referring to, American or International.

Martin, I realize that most SI units predate the formation of the coherent SI system. My point was that you cannot say that people who use the second are using SI, because the second is just as much a part of the English system.

Erin, I don't get the impression that you know very much chemistry.
A mole can be based on any unit of mass. If you accept the SI mole as the standard, as BIPM does, then you are right, the pound-mole is simply an SI mole scaled by the conversion factor of the gram to the pound. But you can also look at it the other way, take the pound-mole as the standard, and use the conversion factor to get the gram-mole.

Neither way makes much sense to me. The most logical way of thinking about it is defining each one in terms of the corresponding unit of mass. However, since some people may be more familiar with the gram-mole, the definition you cited provides the conversion factor in terms of gram-moles.

I have jut done 2 searches on YAHOO. "Pound-mole" gave 303 hits. "Mole" and "Avagadro" gave 48,700 hits. (I added the word "Avagadro" to filter out references to mols that are garden pests).

OK Pound-moles are used, but only by a small minority even in the US!

"""Erin, I don't get the impression that you know very much chemistry."""

I took some chemistry in college as was required, but I'm not a chemistry major. One doesn't have to be to discuss the whether a pound mole is true imperial unit or just a parasite to a metric unit.


"""A mole can be based on any unit of mass."""

But is based on the gram. Any other unit using the name mole is a copy or a deriviative. I would expect an imperial version to at least have a unique name.


"""If you accept the SI mole as the standard, as BIPM does, then you are right, the pound-mole is simply an SI mole scaled by the conversion factor of the gram to the pound. But you can also look at it the other way, take the pound-mole as the standard, and use the conversion factor to get the gram-mole."""


The BIPM and and SI do not use the term gram-mole. They just use the term mole. This unit is the base and even if the other could be, it isn't and never will be. The mole is the only unit used simply because all the laboratories today use gram scales and only SI measuring devices. In addition all the published data is in moles and other SI units so to be able to compare only the SI versions are used.

"""I have jut done 2 searches on YAHOO. "Pound-mole" gave 303 hits. "Mole" and "Avagadro" gave 48,700 hits. (I added the word "Avagadro" to filter out references to mols that are garden pests).

OK Pound-moles are used, but only by a small minority even in the US!"""


I did a google search on pound mole and came up with 547 hits. Just perusing the first couple of pages, none seemed to show actual usage. There was some definintions, a couple relating to what may be a viseo called 90 pound mole, one about having a 148 pound mole removed from someone's ass, etc.

I would think that the pound-mole may have been used in the in the distant past in some areas where pound scales were used to weigh masses. But with the universal usage of metric measuring devices in today's labs only the mole is used.

One thing the imperialists can't seem to grasp is the word REMNANT. That is either an extreme limited amount of usage of an imperial term or a reference to something now obsolete. Nor in other appearances do they grasp the meaning of TRADE NAME. A product that uses imperial terms but the actual dimension isn't even close. Such as vinyl records, wood products and plumbing parts, as an example.

I do laugh at this argument.

I mean think about it.

If I measure how tall my house is in feet and inches then it (i.e. "House Height") CANNOT be measured in metres - so it CANNOT be metric.

What a compelling argument!


----------------


Footnote:- Where in the world does one "major" in a subject.
Folks - think about it.

Martin, you are right, the pound-mole is not used as widely as it once was in the United States. However we are taught to do calculations with it in college, and we use it on projects and exams. I believe the primary place it is still used in the US is the petroleum industry.

"""Martin, you are right, the pound-mole is not used as widely as it once was in the United States. However we are taught to do calculations with it in college, and we use it on projects and exams. I believe the primary place it is still used in the US is the petroleum industry. """

It may have been used there at one time, but petroleum laboratories are up to date and have have been for some time equipped with metric measuring devices. Scales that determine mass in grams, graduated cylinders that are calibrated in millilres, published data only in metric units, etc. would prevent the use of any unit other then the mole.

If it is taught in college it just means some old fogey professor is 40 some years out of step with the real world.

Erin, I don't think you have ever been to a refinery in the United States, or spoken to very many American engineers.
I respect your right to believe whatever you like, but this question is not a matter of opinion.

I have worked in the petroleum industry. As regards the use of units they are a right bunch of cowboys (Is that why Texas rates so high in the petroleum industry).

One of their most stupid units is the "barrels per acre-foot" which, if you use metres when drilling (the norm in the North Sea) is totally meaningless. "Barrles per acre-foot" of course converts to a dimensionless fraction, so one could just as easily say "The rock down there contains 2.4% oil".

Finally, it is worth noting that in the United Kingdom, most engineering bodies are members of the Engineering Council. The most notable exception is the Society of Petroleum Engineers.

"I respect your right to believe whatever you like"

What an excellent way of putting it! nicely worded!





Right, time to put a record on ;-)

Martin, where and when did you work in the petroleum industry?

On and off between 1989 and 2004 at petrophysical laboritories in the UK.

For the benefit of those who don't know the industry, the purpose of petrophyscial laboraties is to analyse oil-bearing rocks so that reservoir engineers can idetnify the optimum way to extract the oil.

"""On and off between 1989 and 2004 at petrophysical laboritories in the UK.

For the benefit of those who don't know the industry, the purpose of petrophyscial laboraties is to analyse oil-bearing rocks so that reservoir engineers can idetnify the optimum way to extract the oil."""


Set the record straight! Were these labs fitted with metric or imperial lab instruments?

Both

Rock samples were measured in cm (not mm as would be the case in other industries).

Pressures were in psi (even though UL legislation requeris that metric units be used for "Public Health" purposes.

Equivalent well depths were given in metres for UK wells and feet for US wells.

Viscosities were measured using cgs units event though MKS is used elsewhere in UK indutry.

I meant the instruments used in the labs to analyse the samples. Like what one would find in any typical lab. Such as mass balances in grams, graduated cylinders and other volume measuring devices in millilitres, thermometeters in degrees Celsius, purchased chemicals in rounded metric quantities, etc.


You and others might find this post from USMA interesting. There may be changes occuring in the oil industry due to international pressure away from American insistance on USC units:

http://www.mail-archive.com/usma@colostate.edu/msg22862.html

In other words, he didn't like your answer, Martin!

<<
I meant the instruments used in the labs to analyse the samples. Like what one would find in any typical lab. Such as mass balances in grams, graduated cylinders and other volume measuring devices in millilitres, thermometeters in degrees Celsius, purchased chemicals in rounded metric quantities, etc.
>>

Apart from pressure gauges, everything that was used in the lab used units that would be found in any UK lab. However, I was required to write one computer program for a piece of equipement that was equiped with rulers in inches, feet and decimals of a foot and metric units.

In another program that I wrote (where I had to verify the physical formulae used myself - my original degree was in Physics), I had to introduce a factor "k" since we were not using SI. (Had we been using SI, "k" would have been unity).

<<
Pressures were in psi (even though UL legislation requeris that metric units be used for "Public Health" purposes.
>>
I really don't think petroleum production has anything to do with public health.


<<
Viscosities were measured using cgs units event though MKS is used elsewhere in UK indutry.
>>
I am not aware of any MKS unit that can be used to measure viscosity. It is necessary to combine units (newton-seconds per metre squared). In the CGS system, there is a separate viscosity unit, the poise.


<<
In another program that I wrote (where I had to verify the physical formulae used myself - my original degree was in Physics), I had to introduce a factor "k" since we were not using SI. (Had we been using SI, "k" would have been unity).
>>
It sometimes works the other way too. For example, if you have the mass of an object and you want to find the force it exerts under standard gravity, in SI you must introduce a g factor. In imperial, it would be 1.

I am not aware of any MKS unit that can be used to measure viscosity. It is necessary to combine units (newton-seconds per metre squared). In the CGS system, there is a separate viscosity unit, the poise.

The correct unit for viscosity in SI is the pascal second (Pa.s)


"""It sometimes works the other way too. For example, if you have the mass of an object and you want to find the force it exerts under standard gravity, in SI you must introduce a g factor. In imperial, it would be 1. """

That is only true if you are defining the pound as a weight unit. In that case your mass unit is slugs. If you are defining a pound as a mass unit, then you need to use a conversion factor to get poundals, which is a force unit. Very confusing!

In SI, the g factor is approximately 10, so for estimating the force on an object it is just 10 times its mass. So a 90 kg man weighs about 900 N. If you are designing a structure to support the weight of 20 000 kg, then designing to support a weight of 200 kN would give you about a 2 % safety factor.


Most formulas used in SI have no fudge factors to make the units work out like imperial does, as all SI units relate to each other 1:1. Example: 1 W = 1 J/s = 1 Nm/s = 1kg m^2/s^2; whereas horsespower needs a fudge factor to convert it to pounds, feet inches and whatever.

Bud wrote

<<
<<<<
Pressures were in psi (even though UK legislation requires that metric units be used for "Public Health" purposes.
>>>>
I really don't think petroleum production has anything to do with public health.
>>

Safety and public health are tied up together and pipes that are subjected to too high a perssure are unsafe.

Don't forget that PSI is all over the place.

... apart from my VW Golf's handbook. (The car itself was an RHD import form France so it has French handbook. I went to the local VW dealer and bought an English handbook. All the technical specifications were in metric units only.

Hmmm, that's a bit daft when you notice that most air-lines are PSI only (and some have bar too).

Did the spec show bar or kg/cm3?

P.S. I was also talking about other places where you get to see PSI, and not just airlines.

It showed bars.

BTW
kg/m^3 is not a measure of pressure since it is not a force per unit area. (psi is really pounds weight per square inch but due to the slap-dash nature of imperial units, it is assumed that everybody (apart from SteveH) knows that they must include thE acceleration due to gravity in their formula.)

The "Pure" SI units is pascals, but bars are an accepted alternative. (1 bar = 100 kPa)

The only bar I know comprises 'pints' as it's base unit of measure.

;-)

Not sure how many pints are in one Bar though - I guess it depends on day of the week and whether students have just received their cheques.

".. everyone ... knows that they must include thE acceleration due to gravity in their formula"

I shall bear that in mind next time my tyres are spinning around as I do (strictly) 70 (or less) on the motorway.

<<
Safety and public health are tied up together and pipes that are subjected to too high a perssure are unsafe.
>>
If that's the way you look at it, then just about everything relates to public health.


<<
The correct unit for viscosity in SI is the pascal second (Pa.s)
>>
Yes, I know that. But a pascal-second and a newton-second per square metre are equivalent.


<<
"""It sometimes works the other way too. For example, if you have the mass of an object and you want to find the force it exerts under standard gravity, in SI you must introduce a g factor. In imperial, it would be 1. """
That is only true if you are defining the pound as a weight unit. In that case your mass unit is slugs. If you are defining a pound as a mass unit, then you need to use a conversion factor to get poundals, which is a force unit. Very confusing!
>>
You can also use pounds mass and pounds force together. Then you don't need any conversion factor or any gravitational acceleration constant. In SI, you need a g factor.
By the way, I have never seen the poundal used anywhere. It was simply a (failed) attempt to "metricise" the English system.


<<
In SI, the g factor is approximately 10, so for estimating the force on an object it is just 10 times its mass. So a 90 kg man weighs about 900 N. If you are designing a structure to support the weight of 20 000 kg, then designing to support a weight of 200 kN would give you about a 2 % safety factor.
>>
In the English system, the factor is one. No need to multiply by anything. If you are designing a structure to support a mass of 20000 lbs, you design it to support a weight of 20000 pounds. See?


<<
kg/m^3 is not a measure of pressure since it is not a force per unit area. (psi is really pounds weight per square inch but due to the slap-dash nature of imperial units, it is assumed that everybody (apart from SteveH) knows that they must include thE acceleration due to gravity in their formula.)
>>
The kilogram-force is often used for certain purposes. I wonder why? Perhaps someone realised that constantly having to multiply by gravitational acceleration to convert mass to force is a pain?

<<
The correct unit for viscosity in SI is the pascal second (Pa.s)
>>
Yes, I know that. But a pascal-second and a newton-second per square metre are equivalent.


The pascal second is a just two terms. The equivalent was used by you to give the appearance of SI being complex by using 5 terms instead of two.


"""You can also use pounds mass and pounds force together. Then you don't need any conversion factor or any gravitational acceleration constant. In SI, you need a g factor.
By the way, I have never seen the poundal used anywhere. It was simply a (failed) attempt to "metricise" the English system."""

There is a conversion factor in imperial it is 32.174 048 56. If a pound is mass, then the mass unit must be divided by this to get poundals, if the pound is weight, then the pound must be multiplied by this to get slugs. A pound mass and pound weight would only equal each other WHERE the "g" factor is unity. The false assumption that mass is equal to force is the result these two distinct physical entities haveing the same unit name in imperial.


"""In the English system, the factor is one. No need to multiply by anything. If you are designing a structure to support a mass of 20000 lbs, you design it to support a weight of 20000 pounds. See?"""

You may be supporting a mass that has a weight of 20 000 pounds, but that doesn't eqaual a mass of 20 00 pounds.



"""The kilogram-force is often used for certain purposes. I wonder why? Perhaps someone realised that constantly having to multiply by gravitational acceleration to convert mass to force is a pain? """


The kilogram force was an attempt to bring the errors of imperial into metric. Imperialists erred by thinking force and mass are the same. The metric side understood it wasn't and correctly established independent units for the different quantities.

Steve

"The only bar I know comprises 'pints' as it's base unit of measure."

Hmmmm

Thought that (horrible) alcopops, bottled beer, smirnoff ice etc & serious nip drinking had overtaken pints/half-pints.

I was in 35ml territory last night. Still haven't recovered!

When I look round my pub it's pint glasses I see mostly.

Maybe your area hasn't moved on from those ghastly alcopops yet?

BTW - In Ireland you can buy pints of Smirnoff Ice (Berenger: "No they don't its a trade name"). Now think how sickly THAT would be!

(I got the other half to nick the glass - i still have it at home, shhh!)

The use of mass units to express force is a pet hate of mine.

American engineers who do this should know better. Their convention for so called English units has the pound-force (strictly written lb-f) derived from the force of gravity (at sea level) acting on a one lb mass.

There are two things wrong with this:

(i) Earth's gravity isn't constant all over the globe even at sea level, so it's badly placed as unit derived from natural constants.

(ii) In stress and load calculations etc, if gravity is present and represents a component force it should be featured explicity in the calculations not hidden in the unit of force.

The same applies to the kg, it should NEVER EVER be used to mean force due to gravity (except colloqually as in "it weighs a kg"). The unit of force is the newton and should be used exclusively for that purpose. Same for pressure, use the pascal (or bar if appropriate) NOT kg/cm^2, kg/m^2 etc.

I'm off to get 200 netwons of gooseburys.

(not in Tesco though ;-) )

P.S. I thought it was "pound foot force" or something.

lb-f foot is a measure of torque or turning force. One example if where (typically) the force is not due to gravity.

In SI it is newton metre, N m.

BTW quite legitimate to say kg of grapes. You are in fact referring to the mass of grapes you are going to buy. "200 newtons of grapes" is meaningless.

BTW quite legitimate to say kg of grapes. You are in fact referring to the mass of grapes you are going to buy. "200 newtons of grapes" is meaningless.


200 N is just 20 kg at sea level and close enough anywhere else on the earth's surface, and if you buy them on the moon, you will get 120 kg. Tesco will happliy sell you 20 kg Steve. Just check your till receipt to make sure you got what you paid for. You don't have to do any conversions as what you as for when asking in kilograms is exactly what you get and is verifiable when you check the receipt.

<<
The pascal second is a just two terms. The equivalent was used by you to give the appearance of SI being complex by using 5 terms instead of two.
>>
I used the newton-metre per second squared because that is what is most commonly used to specify viscosity in MKS units. Erin, find me a single journal or scholarly publication that specifies viscosity in pascal-seconds.



<<
You may be supporting a mass that has a weight of 20 000 pounds, but that doesn't eqaual a mass of 20 000 pounds.
>>
Yes, if you are building it on the moon.
(I added one zero to your mass figure, because I assume it was a typographical error.)


<<
The kilogram force was an attempt to bring the errors of imperial into metric. Imperialists erred by thinking force and mass are the same. The metric side understood it wasn't and correctly established independent units for the different quantities.
>>
The imperialists are more practical. They realised that 99% of all calculations are done with the standard g, so it would be convenient to use this value as the conversion factor between mass and force. The metric system is more scientifically rigorous, but more cumbersome in most cases because calculations require an extra step.

This debate could be the answer to metric's divisibility by 3.

Take your kilogram (in a house where gravity = 1g) & go upstairs to where gravity is slightly less & the Kilo weighs exactly 999.999 repeated grams. Divide your kilogram into perfect thirds & go downstairs again.

You have 1/3 kg !!!!

:-) :-) :-)

"""Take your kilogram (in a house where gravity = 1g) & go upstairs to where gravity is slightly less & the Kilo weighs exactly 999.999 repeated grams. Divide your kilogram into perfect thirds & go downstairs again.""""


Not quite. Even if g = 1 m/s^2 downstairs, then your kilogram would weigh 1 N. If you go upstairs, g becomes 0.99999999...m/s^2, yet you still have a 1 kg mass (mass does not chhange with location), but its weight becomes 999.999 999 mN.


A divide by 3 problem doesn't exist in SI as was explained before. A business that wants to sell a packaged product and also sell 3 equal divisions of that product can easily do so by setting the primary size to a number of grams that can easily be divided by 3. Such as 1200 g. Thus you can have divisions of 300 g, 600 g, 900 g and 1200 g. The simplicity of SI knows no bounds!

For the record, g reduces by about 0.3*10^-6 m/s^2 for every metre that one moves away from the earth's surface.