# 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:** 20\ **Page:** 2
**Author:** ![TipTapTwo](https://avatars.discourse-cdn.com/v4/letter/t/34f0e0/32.png) [@TipTapTwo](https://boards.straightdope.com/u/TipTapTwo)\ **Post date:** [July 1, 2016, 6:53pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/21 "2016-07-01T18:53:47Z")
Side question, why did people decide to define kilogram super accurately, and then say a gram is 1/1000 of that? Why did we not do it the other way around with a super accurate gram and say a kilogram is 1000 of those? In my eyes, starting from a rigorous definition of our smallest units and building up from there, (like basing things around Avogadro’s number and Molarity) would make more sense than creating a silicon sphere (to the best of our limited abilities) and saying “ehh, close enough. Base all of our measurements around this ball.” ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [July 2, 2016, 2:01am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/22 "2016-07-02T02:01:00Z")
> [@Crafter\_Man](#): > > It’s more correct to say the pound is a unit of force. And “weight” is what we call the force when it is due to gravity. > You can’t have a weight of 90 kg. The kilogram is a unit of mass, not weight. If something has a mass of 90 kg on the Earth, it will have a mass of 90 kg on the Moon. Of course, the _weight_ of the object on the Moon will be approximately 1/6th the weight it is on Earth. Yep. If one would use a balance like the one at the doctor’s office, it would even read the same on the moon as it does on Earth, unlike a bathroom spring scale. ---
**Author:** ![Doughbag](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Doughbag](https://boards.straightdope.com/u/Doughbag)\ **Post date:** [July 2, 2016, 10:39am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/23 "2016-07-02T10:39:58Z")
> [@Crafter\_Man](#): > > It’s more correct to say the pound is a unit of force. And “weight” is what we call the force when it is due to gravity. > You can’t have a weight of 90 kg. The kilogram is a unit of mass, not weight. If something has a mass of 90 kg on the Earth, it will have a mass of 90 kg on the Moon. Of course, the _weight_ of the object on the Moon will be approximately 1/6th the weight it is on Earth. Correct kg is a mass, the term kg was used as a commonly used definition to describe a weight on earth. The link I posted with the post should have explained that. ---
**Author:** ![Doughbag](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Doughbag](https://boards.straightdope.com/u/Doughbag)\ **Post date:** [July 2, 2016, 10:41am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/24 "2016-07-02T10:41:17Z")
> [@Leo\_Bloom](#): > > In July 2009 you chose your username in anticipation of this one post? Respect. Thank you! ---
**Author:** ![Doughbag](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Doughbag](https://boards.straightdope.com/u/Doughbag)\ **Post date:** [July 2, 2016, 10:53am UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/25 "2016-07-02T10:53:15Z")
> [@Crafter\_Man](#): > > It’s more correct to say the pound is a unit of force. And “weight” is what we call the force when it is due to gravity. The pound is a [mass](https://en.wikipedia.org/wiki/Pound_(mass)) and a [force](https://en.wikipedia.org/wiki/Pound_(force)) If you’re nitpicking a post, at least be correct yourself. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 2, 2016, 12:38pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/26 "2016-07-02T12:38:05Z")
Yes, there are units of mass and force which are both called “pound”. They are two completely different units, and cannot be compared. And it was idiotic to set up a system (or mishmash of systems) where two different units could be assigned the same name like that. In fact, one might even say that those who set up that mishmash of systems did it wrong. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [July 2, 2016, 1:05pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/27 "2016-07-02T13:05:18Z")
> [@TipTapTwo](#): > > Side question, why did people decide to define kilogram super accurately, and then say a gram is 1/1000 of that? Why did we not do it the other way around with a super accurate gram and say a kilogram is 1000 of those? > > In my eyes, starting from a rigorous definition of our smallest units and building up from there, (like basing things around Avogadro’s number and Molarity) would make more sense than creating a silicon sphere (to the best of our limited abilities) and saying “ehh, close enough. Base all of our measurements around this ball.” Because in the [SI system of units](https://en.wikipedia.org/wiki/SI_base_unit), it’s indeed the kilogram that’s the base unit, with the gram being derived from that. As to why it’s got a prefix, with the gram being prefix-less, while with all the other base unit, they’re prefix-less and derived units are built using prefixes, I have no idea. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 2, 2016, 1:32pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/28 "2016-07-02T13:32:44Z")
> [@Chronos](#): > > Yes, there are units of mass and force which are both called “pound”. They are two completely different units, and cannot be compared. Agree. When you hear the word “pound,” you should not think of mass. You should think of _force_. ---
**Author:** ![Doughbag](https://avatars.discourse-cdn.com/v4/letter/d/aeb1de/32.png) [@Doughbag](https://boards.straightdope.com/u/Doughbag)\ **Post date:** [July 2, 2016, 2:21pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/29 "2016-07-02T14:21:47Z")
> [@Crafter\_Man](#): > > Agree. > > When you hear the word “pound,” you should not think of mass. You should think of _force_. That naming system is a complete and utter mess. It doesn’t matter what you think people should think of what “pound” means, since it’s clearly a definition for “force”, “mass” and oddly also a “currency”. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [July 2, 2016, 3:21pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/30 "2016-07-02T15:21:12Z")
> [@Doughbag](#): > > That naming system is a complete and utter mess. > > It doesn’t matter what you think people should think of what “pound” means, since it’s clearly a definition for “force”, “mass” and oddly also a “currency”. And the application of force, and dog prison. ---
**Author:** ![coffeecat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coffeecat/32/3405_2.png) [@coffeecat](https://boards.straightdope.com/u/coffeecat)\ **Post date:** [July 2, 2016, 3:50pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/31 "2016-07-02T15:50:08Z")
Trivia: The unit of mass in the U.S. customary system is the **slug**. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [July 2, 2016, 4:24pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/32 "2016-07-02T16:24:45Z")
Force, mass, weight, silicon, planks, avocados, slugs…enough! Can’t you people just get a good scale? What situation requires the degree of accuracy you describe? ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 2, 2016, 5:10pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/33 "2016-07-02T17:10:52Z")
> [@Crafter\_Man](#): > > Agree. > > When you hear the word “pound,” you should not think of mass. You should think of _force_. No, you should think of plucky little England, free at last: **Butcher starts selling meat in imperial pounds and ounces after Britain ditches the EU** > **[Butchers starts selling meat in imperial pounds & ounces after Brexit](https://www.express.co.uk/news/uk/683451/Brexit-EU-European-Union-Referendum-Grattons-Butchers-Devon-Britain-Metric-imperial-pounds)** > > A BUTCHER has started selling meat in pounds and ounces for customers fed up of the metric system following the Brexit vote. ETA: Just realized “plucky” is a double entendre in this context. Witty me! ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [July 3, 2016, 2:27pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/34 "2016-07-03T14:27:26Z")
> [@Leo\_Bloom](#): > > No, you should think of plucky little England, free at last: > > **Butcher starts selling meat in imperial pounds and ounces after Britain ditches the EU** > > [Butcher starts selling meat in pounds and ounces after Britain votes Brexit | UK | News | Express.co.uk](http://www.express.co.uk/news/uk/683451/Brexit-EU-European-Union-Referendum-Grattons-Butchers-Devon-Britain-Metric-imperial-pounds) I have no problem with this as long as he charges his customers £2.3s.6d for the meat. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [July 3, 2016, 3:34pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/35 "2016-07-03T15:34:35Z")
Good publicity stunt - I buy meat at my local supermarket and often ask for 4oz of ham, or ½lb of mince etc. The butcher simply converts in his head and sells me the amount I want. It is priced in £ per K but I get the weight I want so I am happy and no laws are broken. OH - the laws on weights and measures are British as we officially went metric by 1980, with a few exceptions - milk, beer and roads come to mind. This bought to an end (more or less) a process that had been going on for the best part of a hundred years. ---
**Author:** ![nate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nate/32/13085_2.png) [@nate](https://boards.straightdope.com/u/nate)\ **Post date:** [July 3, 2016, 4:15pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/36 "2016-07-03T16:15:07Z")
I frequently interact with the team at NIST that is doing the watt balance experiment. It’s rather impressive looking to see in person. I’m an idiot compared to these guys, but it seems to me to be a rather error-prone and overly complex way to represent the kg… IMHO the overall idea is not very clever or novel, it’s more like a brute-force method to take the ancient idea of a physical balance but make every component super-accurate and “known”. There’s little creativity in the overall design. The individual components are culminations of decades of development and are mature in their own areas of use and these components are used together to create some ancient apparatus. I say it’s error-prone, but they know what most of the errors are and correct for them, but it seems rather finicky if a car parks over the building (the watt-balance is underground) and it changes the local gravity enough to cause a shift in measurement. Again, they correct for this, but it seems like a job of corralling cats. By the way, here is a video from NIST showing you how to build your own watt-balance from legos: [http://www.nist.gov/pml/nist-diy-watt-balance.cfm](http://www.nist.gov/pml/nist-diy-watt-balance.cfm) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 3, 2016, 6:11pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/37 "2016-07-03T18:11:39Z")
That’s nothing compared to what the gravitational wave folks need to go through. Forget cars-- the LIGO instruments can actually detect noise from the gravitational effects of tumbleweeds blowing past. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 3, 2016, 7:10pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/38 "2016-07-03T19:10:54Z")
Neat. I seem to recall some nudnik on this board asking for someone to figure out the amount of curvature of a beam of light around him due to his mass. ETA: never got an answer. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 3, 2016, 9:07pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/39 "2016-07-03T21:07:22Z")
As far as I understand after a too-quick read of Wiki kilogram article, the bulk of the reference articles gain mass periodically, except for one case where it’s losing mass and no-one can figure out just why. Sort of a hijack, but only sort of: The gains in mass can come from adsorption, and adsorption of mercury was cited in one case, because of the proximity of a thermometer (I have in mind one like the ones that go up a baby’s butt, although it’s probably different) with/using that element. How do mercury atoms “outgas?” Is it, then, that the insert-in-mouth-or-butt thermometer in my medicine chest is leaking mercury atoms also? ---
**Author:** ![MaxTheVool](https://avatars.discourse-cdn.com/v4/letter/m/9fc29f/32.png) [@MaxTheVool](https://boards.straightdope.com/u/MaxTheVool)\ **Post date:** [July 4, 2016, 5:27pm UTC](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828/40 "2016-07-04T17:27:36Z")
So can someone explain what will actually be done with this super-precise new scale once it exists? What day-to-day operations will it be used for, if any? [Previous page](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828.md?page=1) [Next page](https://boards.straightdope.com/t/how-to-determine-a-kilogram/758828.md?page=3)