How come weight difference doesn't cause problems in trade?

[Andreas C]

This is not strictly a physics question, I just figured this is the best place to ask it.

I think everyone is familiar with the subtle difference in the effects of gravity from the poles to the equator. At or near the equator, objects weigh about 0.5% less than they do at or near the poles. My question is, how come this doesn't cause any problems in trade?

Let me explain: say you run a company based on the Netherlands or Sweden or some place similar and another company based in some country near the equator orders 10kg of something precious, say gold. You weigh it precisely, but when it is shipped to whomever ordered it, guess what he will tell you: "Look, you a-holes, I ordered precisely 10kg, but received 9.95kg instead, are you trying to scam me?".

I guess that if I owned a big business I would be bummed to know that I consistently lose 0.5% of my earnings in that manner! How come there exist no such problems?

 

[mfb]

Trades happen based on mass (kg), not on weight (N). Scales have to be adjusted to their location if the precision requires that.

 

[FactChecker]

Good question. Maybe they calibrate their scales using standard weights that have undergone the same weight reduction.

 

[Andreas C]

Trades happen based on mass (kg), not on weight (N). Scales have to be adjusted to their location if the precision requires that.

Yes, I know, but I have never heard of scales adjusted to the location. Do you have any additional information on that?

 

[Andreas C]

Good question. Maybe they calibrate their scales using standard weights that have undergone the same weight reduction.

Yeah, maybe they have a standard set of weights that they use to calibrate them, but I can't find much information on that. It would also be very bad if someone took the scale and transported it somewhere else.

 

[DrClaude]

Yes, I know, but I have never heard of scales adjusted to the location. Do you have any additional information on that?

Yeah, maybe they have a standard set of weights that they use to calibrate them, but I can't find much information on that. It would also be very bad if someone took the scale and transported it somewhere else.

You should first read about the prototype kilogram and its copies: https://en.wikipedia.org/wiki/Kilogram#International_prototype_kilogram

In most countries, there is a standards institute responsible for certifying scales. That institute will have some standard masses that they use to calibrate their instruments and that will be used to certify that a scale is properly adjusted for use in trade.

 

[Andreas C]

You should first read about the prototype kilogram and its copies: https://en.wikipedia.org/wiki/Kilogram#International_prototype_kilogram

In most countries, there is a standards institute responsible for certifying scales. That institute will have some standard masses that they use to calibrate their instruments and that will be used to certify that a scale is properly adjusted for use in trade.

That makes sense, but what happens when a scale is transported?

 

[Bystander]

It has to be re-calibrated.

 

[Merlin3189]

Yeah, maybe they have a standard set of weights that they use to calibrate them,...

So what would a standard weight look like?
A standard mass is a solid block, but could you make a standard weight like that? Wouldn't its weight vary from place to place and maybe from time to time as the Earth rotated beneath the moon?
I guess a standard weight might be a spring stretched to a certain distance or maybe a pair of coils at a certain spacing with a certain current flowing. Are there any others in common use?

 

[DrGreg]

Where people have said "standard weight" in this thread, they should really have said "standard mass".

If you use a "balance scale" instead of a spring-based scale, it doesn't need recalibration when you move it.

 

[mfb]

There is no standard weight, and no need for that. Devices that can measure accelerations can easily be transported, and masses can be transported as well, both combined allows to calibrate force measurements.

 

[Andreas C]

It has to be re-calibrated.

Ah ok then.

 

[Andreas C]

Where people have said "standard weight" in this thread, they should really have said "standard mass".

If you use a "balance scale" instead of a spring-based scale, it doesn't need recalibration when you move it.

Sure, but balance scales are a bit old school, no longer used. When I'm saying "standard weight", I mean the object. Of course it's a standard mass, but for whatever reason, the objects are called weights.

 

[Andreas C]

There is no standard weight, and no need for that. Devices that can measure accelerations can easily be transported, and masses can be transported as well, both combined allows to calibrate force measurements.

I know they CAN be transported, I just didn't know if they ARE transported in reality.

 

[epenguin]

With the simplest of weight measurement devices - old fashioned two-arm balance - you don't need to recalibrate a thing. You just need to take the box of weights authorised directly or indirectly at the original Standards institute and it works for all commercial purposes and most others without any worries or adjustment just the same anywhere on earth, also on Mars and many other places.

 

[Andreas C]

With the simplest of weight measurement devices - old fashioned two-arm balance - you don't need to recalibrate a thing. You just need to take the box of weights authorised directly or indirectly at the original Standards institute and it works for all commercial purposes and most others without any worries or adjustment just the same anywhere on earth, also on Mars and many other places.

Yes, but as I've said, balance scales are no longer widely used.

 

[mfb]

That doesn't really matter, putting test mass 1 on the scale and then putting test mass 2 on the scale to compare has the same effect.

 

[sophiecentaur]

An ideal standard of measurement should be specified in such a way that anyone (planet Zog) should be able to produce it with no more than a piece of paper which tells them how to produce it. Time and length are both referred to atomic standards - spectral lines and frequencies. Unfortunately, the inhabitants of planet Zog would have no access to standard (or sub standard) kg masses in Paris. There is a lot of work (See this wiki link) on finding a reliable way to assemble a known number of atoms of an element to produce a universal standard of mass. That process seems to be a lot more fraught than looking at a simple Hydrogen line. The Zoggians are still waiting for information how to get their own personal 1kg for laboratory use.

 

[Andreas C]

That doesn't really matter, putting test mass 1 on the scale and then putting test mass 2 on the scale to compare has the same effect.

I don't disagree, it's just that I didn't know to what extent that was done in trade.

 

[Andreas C]

An ideal standard of measurement should be specified in such a way that anyone (planet Zog) should be able to produce it with no more than a piece of paper which tells them how to produce it. Time and length are both referred to atomic standards - spectral lines and frequencies. Unfortunately, the inhabitants of planet Zog would have no access to standard (or sub standard) kg masses in Paris. There is a lot of work (See this wiki link) on finding a reliable way to assemble a known number of atoms of an element to produce a universal standard of mass. That process seems to be a lot more fraught than looking at a simple Hydrogen line. The Zoggians are still waiting for information how to get their own personal 1kg for laboratory use.

I remember hearing about an experiment involving a near perfect pure silicon sphere that weighs exactly 1kg, where there was effort trying to measure the silicon atoms contained inside the sphere so that the kilogram will no longer have to be defined based on a set of standard weights. Instead, we would say "1kg is defined to be the mass of n atoms of silicon" to the Zoggians, and their problem would be solved! Provided of course that they can weigh a precise number of silicon atoms...

 

[sophiecentaur]

Provided of course that they can weigh a precise number of silicon atoms...

There's always the possibility that the Zoggians will tells us how to do it!

 

[Andreas C]

There's always the possibility that the Zoggians will tells us how to do it!

Nah, I'm pretty sure the Zoggians are pretty dumb. Why else would they name themselves or at least accept being called that name?

 

[sophiecentaur]

I believe it is a great compliment in their language. The phrase 'Earth man", on the other hand, is synonymous with "dung beetle".

 

[Andreas C]

I believe it is a great compliment in their language. The phrase 'Earth man", on the other hand, is synonymous with "dung beetle".

That's not entirely inaccurate.

 

[sophiecentaur]

That's not entirely inaccurate.

when applied to 'other' Earth men, perhaps.

 

[Andreas C]

when applied to 'other' Earth men, perhaps.

Do you mean I am excluded from that? Awww thanks!

 

[epenguin]

I remember hearing about an experiment involving a near perfect pure silicon sphere that weighs exactly 1kg, where there was effort trying to measure the silicon atoms contained inside the sphere so that the kilogram will no longer have to be defined based on a set of standard weights. Instead, we would say "1kg is defined to be the mass of n atoms of silicon" to the Zoggians, and their problem would be solved! Provided of course that they can weigh a precise number of silicon atoms...

I think they don't weigh, them they count them. Then as the silicon atoms are the same here and somewhere else, including planet Zog, You can define 1 Kg as so many silicon atoms and your definition of a Kg and the possibility of realising a measurement don't depend on transporting any physical object from one place to another - that thing can be realized independently in one place or another, you don't have to depend on a precious thing you vainly hope is unchanging in a vault in Paris.

 

[FactChecker]

Yes, but as I've said, balance scales are no longer widely used.

I think that balance scales are used more than you might realize. The doctor's office scale comes to mind. But I still agree with your basic point and I didn't realize that the percent error was so large (about 0.5% "lighter" at the Equator than at the North Pole). Maybe the people who do the weighing know to adjust for it. Keep in mind that the error at the Netherlands (Latitude =~ 52 deg) would be smaller, about 0.3%.

 

[Andreas C]

I think they don't weigh, them they count them. Then as the silicon atoms are the same here and somewhere else, including planet Zog, You can define 1 Kg as so many silicon atoms and your definition of a Kg and the possibility of realising a measurement don't depend on transporting any physical object from one place to another - that thing can be realized independently in one place or another, you don't have to depend on a precious thing you vainly hope is unchanging in a vault in Paris.

If you want to do anything practical with the unit, at some point you will need to make a physical object with the same mass as that number of silicon atoms.

 

[Andreas C]

I think that balance scales are used more than you might realize. The doctor's office scale comes to mind. But I still agree with your basic point and I didn't realize that the percent error was so large (about 0.5% "lighter" at the Equator than at the North Pole). Maybe the people who do the weighing know to adjust for it. Keep in mind that the error at the Netherlands (Latitude =~ 52 deg) would be smaller, about 0.3%.

I mentioned the Netherlands because of the low altitude, which would bring it even closer to the center of earth.

 

[jbriggs444]

Maybe the people who do the weighing know to adjust for it.

See post #8. Or look at this article. http://www.bittermanscales.com/blog/scale-calibration

[attribution repaired]

 

[DrGreg]

DrGreg said: ↑
Maybe the people who do the weighing know to adjust for it.

See post #8. Or look at this article. http://www.bittermanscales.com/blog/scale-calibration

It wasn't me who said that!(Now fixed!)

 

[epenguin]

If you want to do anything practical with the unit, at some point you will need to make a physical object with the same mass as that number of silicon atoms.

Yes, I am saying nothing different from that.

 

[Merlin3189]

...and I didn't realize that the percent error was so large (about 0.5% "lighter" at the Equator than at the North Pole). ...

Yes, I too was surprised by the size of difference. But in the world of commerce I think that is still very small.
In the UK most Wights & Measures legislation is intended to protect individual retail purchasers, who may not have the ability to check their purchases. The principle of caveat emptor is generally assumed to apply to transactions between peer businesses. It would be a matter of contract when there was a disagreement over the quantity supplied.

I don't know if businesses may agree any sort of measure between them, but for retail trade only legally specified "weights" must be used and these are all defined in terms of SI mass, so that there can be no ambiguity, disagreement, nor variation. (Eg. "the pound shall be 0·453 592 37 kilogram exactly." ,“OUNCE TROY = 0.031 103 476 8 kilogram.”;)

As for error the worst case I've found so far is a permissible 9% underweight for small packs sold by nominal average weight and provided that the average weight over a batch is at or above the marked value. This is clearly intended to address the manufacturer's difficulty in accurately controlling and measuring economically, rather than permitting unfair trading. Generally the tolerances are much smaller. For non-packaged goods the general principle is that underweight is not permissible and reasonable overweight is allowed to the extent necessary to avoid the possibility of being underweight. (As far as I can tell, excessive overweight would be an offence!) Using unapproved or seriously inaccurate weighing equipment would be an offence, even if there were no underweight sale.

say you run a company based on the Netherlands or Sweden or some place similar and another company based in some country near the equator orders 10kg of something precious, say gold. You weigh it precisely, but when it is shipped to whomever ordered it, guess what he will tell you: "Look, you a-holes, I ordered precisely 10kg, but received 9.95kg instead, are you trying to scam me?".

Our (UK) Wights & Measures specifically exempts dealings with foreigners! If we sell on goods from other UK (and, at the moment EU) suppliers, we can reasonably rely on their warranty as to packed quantities, but we are expected to check deliveries from foreigners.
If you had contractually specified weight rather than mass, then you obviously ought to have specified a little more carefully where it should be measured. If Free On Board or EXWorks presumably weighing at that point would be implied and you would have specified any variation such as weighing at destination. I really can't see that you have any complaint.

 

[Andreas C]

To be frank, you confused me now...