A bit below comes a question from an informatics layman. (01)
Gunther Schadow wrote: (02)
> ingvar_johansson wrote:
>> one more comment. You asked:
>>
>>> 1 N.m = 1 N.m : true or false?
>>
>> and I said 'true' (and so did Pat H). But this does not imply that 1 N.m
>> of energy = 1 N.m of moment of force, since energy and moment of force
>> are
>> different kinds of quantities (despite having the same dimension).
>
> and that's precisely my point and why I disagree with Pat Hayes
> that this is not useful. I was asking if 1 N.m = 1 N.m and
> the answer is ambiguous. The unit is newton-meter, it is not
> newton-meter-of-energy, therefore, I would argue, that the unit
> is the same even if the kinds of quantity are different. Unless
> we agree on this (by either one of us changing our mind) I don't
> see a value at looking at ontological constructs.
>
> I don't want to discuss the N.m issue in particular at this
> time, only that it's pointless to proceed if there is
> disagreement about this matter.
>
> The question remains what we believe jointly that UoM concepts
> should do for us. You may want them to preserve the difference
> between torque and energy, I don't. (03)
Can't you both cancel and preserve the difference? That is, can't you have
both an over-arching concept 'nominal newton-meter' and a number of
subsumed concepts such as 'energy newton-meter' and 'torque newton-meter';
each of which brings in what VIM calls a kind-of-quantity? (04)
Ingvar (05)
> So the question remains
> open on the list. But there is no point in proceeding if we
> don't agree on this. We might, however, agree if we use these
> example to be more clear about why we have the desire for the
> UoM concepts to do what we want them to do and possibly how
> else we might get our desires fulfilled.
>
> In my experience with dealing with scientific equations and
> computations, the units were incredibly useful for (a) converting
> to a unit that I needed and (b) giving assurance that I probably
> didn't make some gross error in my equations. Thus, in my
> experience with dimensioned terms it does not matter in the end
> whether the m in N.m, was the length of a lever or a distance
> of displacement, that is all in the concerns that led to my
> equations. The units function more like a check-digit at the
> end: if the unit term does not agree with the expected kind of
> quantity, something went wrong in my calculation or the formula.
>
> This is why around UCUM implementation I use the concept of
> a "DimensionedQuantity". A Quantity is any set of values
> where at least some values have a difference operation. A
> DimensionedQuantity is essentially a number with a dimension.
> Such a quantity for example is 16 N.m. Units are themselves
> DimensionedQuantities with a name (and the name can be complex
> such as N.m or even 16.N.m) So, my ontology behaves exactly
> like the symbols that I write on a sheet of blank paper when
> I compute my scientific equations. It does not do more nor
> less than what the units do on paper. I.e., 1 N.m = 1 N.m
> = 1 kg.m2.s-2 = 1 J.
>
> There is nothing you can do to separate these concepts unless
> by assuming into your theory the detail of all of mechanics
> (and all of science) which you can't do.
>
> BTW, it is not true that N.m of torque and joule of energy
> are completely unrelated. Because the torque times angle
> moved is again your energy. Whether or not we maintain a
> dimension for angle in UCUM is also besides this point. Of
> course: by adding more distinct dimensions we may be able
> to preserve more distinctions and by having less dimensions
> we lose distinctions that we can make by just looking at
> number and unit. But because I do not expect much more than
> the function of a "dimensional check digit" and defined
> conversion rates from the units, I can give or take a few
> dimensions without much trouble. The only place were I really
> get into trouble is where we haven't even started to discuss,
> i.e., idiosyncratic "procedure defined units".
>
> regards,
> -Gunther
>
> --
> Gunther Schadow, M.D., Ph.D. gschadow@xxxxxxxxxxxxxxx
> Associate Professor Indiana University School of Informatics
> Regenstrief Institute, Inc. Indiana University School of Medicine
> tel:1(317)423-5521 http://aurora.regenstrief.org
>
> _________________________________________________________________
> Message Archives: http://ontolog.cim3.net/forum/uom-ontology-std/
> Subscribe: mailto:uom-ontology-std-join@xxxxxxxxxxxxxxxx
> Config/Unsubscribe:
> http://ontolog.cim3.net/mailman/listinfo/uom-ontology-std/
> Shared Files: http://ontolog.cim3.net/file/work/UoM/
> Wiki: http://ontolog.cim3.net/cgi-bin/wiki.pl?UoM_Ontology_Standard
>
> (06)
_________________________________________________________________
Message Archives: http://ontolog.cim3.net/forum/uom-ontology-std/
Subscribe: mailto:uom-ontology-std-join@xxxxxxxxxxxxxxxx
Config/Unsubscribe: http://ontolog.cim3.net/mailman/listinfo/uom-ontology-std/
Shared Files: http://ontolog.cim3.net/file/work/UoM/
Wiki: http://ontolog.cim3.net/cgi-bin/wiki.pl?UoM_Ontology_Standard (07)
|