# How To Determine a Kilogram **URL:** \ **Category:** Factual Questions\ **Created:** [June 30, 2016, 9:17pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828 "2016-06-30T21:17:59Z")\ **Posts on this page:** 4\ **Page:** 6
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [November 29, 2018, 3:48am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/101 "2018-11-29T03:48:41Z")
> [@Irishman](#): > > I came across this in college once, but SI doesn’t use the kilopond or kilogram-force. The SI unit of force _is_ the Newton. SI was adopted in 1960, the Newton was adopted as the unit of force in 1946 as part of the MKS system (although it wasn’t named for two more years until after the war). The earlier Metric CGS unit of force was the _dyne_ which is still in use by people such as CERN and the ESA. The kilopond was prohibited through (Directive 71/354/EEC), Annex, Chapter III > [@](#): > > Member States shall, with effect from 31 > December 1977 at the latest, prohibit the use of the > units of measurement listed in Chapter III of the > Annex. > [@Irishman](#): > > The root of this problem is the history of how the terms originated. The pound was originally a measure of force and mass - they were considered the same thing. With Newton came the understanding of the difference, and the need to separate the units because the relationship is offset by the acceleration of gravity (standard 32.2 ft/sec[sup]2[/sup]). Slugs aren’t the problem, the problem is the pound mass. Whenever you use that, you have to use a conversion factor, 32.2 ft-lbm/lbf-sec[sup]2[/sup]. Initially the “gram,” which was the original base unit was defined as the mass of one cubic centimeter at the temperature of greatest density. The mid century shift was a return to the units of “ones” and not exclusively an attempt to go scientific. > [@Irishman](#): > > A mole is a count of matter, which is a form of amount. Mass is a different measure of amount - the resistance to acceleration. Ignore that whole thing, too many straw-men to account for. You are just re-iterating my earlier point in the thread there. > [@Irishman](#): > > If you are trying to determine the amount of rocket fuel, you definitely need mass. You have to account for the mass of the fuel that is being used, and the momentum transfer. Straw-man, I have no problem with the concept of mass, nor did I EVER say above it was useless. Yes…and comparing the kilogram standards have always required “weighing” them as that is what scale are, systems which compare forces. Now to derive the kilogram you have to actually “weigh” things. And no, Newton himself isn’t the cause of “Mass/Weight” confusion, it is those who use theories have been superseded to deny that today; an objects inertial-mass and gravitational-mass are known to be measures of the exact same fundamental property. Feel free to disprove inertial mass and gravitational weight are equivalent. You would disprove General Relativity and probably get a Nobel if you can. The almost systemic \*fervent denial \*of 100 years of experimental tests and verification of Einstein’s Equivalence Principle by pop-science is the problem, not the base unit. The kilogram is great, denying an objects inertial-mass and gravitational-mass are fundamentally the same property is the issue. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [November 29, 2018, 5:26pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/102 "2018-11-29T17:26:08Z")
> [@rat\_avatar](#): > > SI was adopted in 1960, the Newton was adopted as the unit of force in 1946 as part of the MKS system (although it wasn’t named for two more years until after the war). The earlier Metric CGS unit of force was the _dyne_ which is still in use by people such as CERN and the ESA. None of which changes what I said. And yes, I’m aware that the dyne is still used by certain groups using CGS system. You do know the history better than I do. > [@](#): > > Initially the “gram,” which was the original base unit was defined as the mass of one cubic centimeter at the temperature of greatest density. The mid century shift was a return to the units of “ones” and not exclusively an attempt to go scientific. I’m not sure what that means. > [@](#): > > Ignore that whole thing, too many straw-men to account for. You are just re-iterating my earlier point in the thread there. It’s a subtle disagreement over what the term “amount” means. I submit that it is an ambiguous term. The BIMP page agrees, saying that concentration is also an amount. > [@](#): > > And no, Newton himself isn’t the cause of “Mass/Weight” confusion, it is those who use theories have been superseded to deny that today; an objects inertial-mass and gravitational-mass are known to be measures of the exact same fundamental property. I see no one in this thread denying that. You have built a straw man. Once Newton defined the relationship between force and mass, people had to decide what having a pound of something meant. Was that a mass or a force unit? They chose to make it both, but mathematics said they couldn’t be the same thing. I agree that the way to measure mass requires a force. A balance scale still uses force. Mass is a measure of reaction to acceleration, which is wholly determined by amount of matter involved. I suppose that one could argue that mass is a surrogate for amount of matter, just like weight is a surrogate for amount of mass. A kilogram of carbon and a kilogram of gold both have mass of one kilogram, but the number of items (atoms) making up each one is different. That’s where count comes in. Count the particles in moles. Getting the mass from the count requires knowing the molecular mass of the substance in question. Just like getting the weight from the mass requires knowing the gravity acceleration. None of which changes the fact that to use pounds as a force _and_ a mass unit requires a conversion factor. That conversion factor is an artifact of the units chosen given the relationship between the properties. Nor does it change the fact that mass is invariant of the acceleration field, while weight/force requires it. One can give the output from a spring scale in units of kilograms. That requires using an inherent conversion factor of assumed acceleration. For many uses in everyday life, that is sufficient. It is, however, technically wrong to say you weigh X kg. Although historically and colloquially, _weigh_ is often used for measuring mass. It’s not scientifically correct. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [November 29, 2018, 6:13pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/103 "2018-11-29T18:13:39Z")
> [@Irishman](#): > > None of which changes what I said. And yes, I’m aware that the dyne is still used by certain groups using CGS system. You do know the history better than I do. > > I’m not sure what that means. > > It’s a subtle disagreement over what the term “amount” means. I submit that it is an ambiguous term. The BIMP page agrees, saying that concentration is also an amount. > > I see no one in this thread denying that. You have built a straw man. > > Once Newton defined the relationship between force and mass, people had to decide what having a pound of something meant. Was that a mass or a force unit? They chose to make it both, but mathematics said they couldn’t be the same thing. > > I agree that the way to measure mass requires a force. A balance scale still uses force. Mass is a measure of reaction to acceleration, which is wholly determined by amount of matter involved. > > I suppose that one could argue that mass is a surrogate for amount of matter, just like weight is a surrogate for amount of mass. A kilogram of carbon and a kilogram of gold both have mass of one kilogram, but the number of items (atoms) making up each one is different. That’s where count comes in. Count the particles in moles. Getting the mass from the count requires knowing the molecular mass of the substance in question. Just like getting the weight from the mass requires knowing the gravity acceleration. > > None of which changes the fact that to use pounds as a force _and_ a mass unit requires a conversion factor. That conversion factor is an artifact of the units chosen given the relationship between the properties. > > Nor does it change the fact that mass is invariant of the acceleration field, while weight/force requires it. > > One can give the output from a spring scale in units of kilograms. That requires using an inherent conversion factor of assumed acceleration. For many uses in everyday life, that is sufficient. It is, however, technically wrong to say you weigh X kg. Although historically and colloquially, _weigh_ is often used for measuring mass. It’s not scientifically correct. A balance scale compares masses through the use of force without knowing gravity. The [kibble balance](https://www.nist.gov/si-redefinition/kilogram-kibble-balance) compares the force _under gravity_ and compares forces by _weight_ and is now the official way of finding the kilogram. In a gravitational system, **the unit of force** is a base unit, and the unit of mass is derived from it. In an absolute system, the unit of mass is a base unit, and the unit of force is derived from it. US Customary, Imperial and the Metric systems are _all_ absolute systems. If you disagree with this feel free to provide a cite that this is not true. The pound or pound-mass is the unit of mass used in the imperial, United States customary. I have provided multiple links as to such, and as the loss of precision due to changing gravity on the earth is fairly small, defining a _derived unit_ of mass-force under the acceleration of typical gravity works for ‘weight’ and is useful for. Yes mass is a measure of resistance to acceleration, but it is not _wholly determined by amount of matter involved_. It also depends on how the parts are arranged and their energy content. [ul] [li]Nuclei are made up of protons and neutron, but the mass of a nucleus is _always_ less than the sum of the individual masses.[/li][li]Molecules are made up of individual atoms, but the mass of a molecule is _always_ less than the sum of the individual masses.[/li][li]Protons are made up of individual quarks, but the mass of a proton is _always_ **more** than the sum of the individual masses.[/li][/ul] If you have 1000 individual grains of sand, and they are separated by a great distance in empty space they will have more _mass_ than if you rearrange them into a ball. The new configuration has a different energy than the old, and a small amount of energy was freed up due to a loss in potential energy when you bring them together. Another example, say you have a mechanical watch which stopped as you haven’t wound it for a while and you “count” the particles and measure it’s mass. If you then wind the spring, increasing potential energy and the gears start to move producing thermal energy etc… It will still have the exact same “count” of particles or matter or stuff, which every you prefer, but the energy required to move it (mass) will have gone up. Mass is simply just not invariant across changes in energy, which includes changes in energy due to configuration. Mass is that quantity that is solely dependent upon the inertia of an object. It is not a measure of physical substance in general. The property that is _mass_ is exactly the same if it is measured via a rotating torsion balance or a typical balance scale. And while this property is useful for dividing quantities it is not a measure of the quantity of “matter” at all. Feel free to provide cites if you want to argue against the weak equivalence principle. But we have experimental evidence that it holds to _at least_ 10[sup]−17[/sup]. Here is a recent example [[1710.05860] Multimessenger tests of the weak equivalence principle from GW170817 and its electromagnetic counterparts](https://arxiv.org/abs/1710.05860) ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [November 29, 2018, 7:34pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/104 "2018-11-29T19:34:38Z")
To keep the systems clean, it might have been better to keep the poundal instead. > **[Poundal](https://en.wikipedia.org/wiki/Poundal)** > > The poundal (symbol: pdl) is a unit of force, introduced in 1877, that is part of the Absolute English system of units, which itself is a coherent subsystem of the foot–pound–second system. > The poundal is defined as the force necessary to accelerate 1 pound-mass at 1 foot per second per second. > 1 pdl = 0.138254954376 N exactly. > English units require re-scaling of either force or mass to eliminate a numerical proportionality constant in the equation F = ma. The poundal represents one choice, whi... The rest I will have to contemplate. [Previous page](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828.md?page=5)