On Wed, September 26, 2012 11:44, Andries van Renssen wrote:
> John F Sowa on 26 september 2012 at 15:53 wrote:
>> On 9/26/2012 8:53 AM, Andries van Renssen wrote:
>> ...
>> > But the piece of land that is defined by that boundary is
>> > nevertheless a physical object, and it has a mass, although
>> > its value is unknown and not of interest. (01)
>> Space is physical, but it doesn't have a mass. An area is
>> a two-dimensional region. The political subdivisions only
>> specify coordinates that determine the area at the surface,
>> and they are silent about depth or height. (02)
> [AvR] I hesitate about the mass of a physical space, and whether the gas
> in a space is part of the space or just occupies the space. (03)
Occupies. (04)
> But if the space is
> not empty, the mass may be of interest such as in the interior of a
> balloon and a submarine. (05)
Sure. (06)
> ...
> I question whether a physical area is by definition two dimensional. (07)
I'm not sure what you mean by "physical area". (08)
> Mathematical area's are two dimensional. But two dimensional area's in
> physical reality seem to be abstractions. They are at least curved in the
> third dimension. (09)
Fine. Math allows this. Iit also defines planar 2D areas. (010)
> But more important: if you walk on them, they compress
> under pressure and they provide an upward force on you. (011)
The areas don't compress. The physical surface does. (012)
> If you buy them (013)
You don't buy an area (or volume). You buy physical land or part of
a physical structure or rights to take certain actions within some
volume (spatial or physical). (014)
> then you also possess a mass with volume below and a space above it, (015)
If you buy a physical object, then you own (a social property) the mass
that comprises that object along with associated rights as defined by
society. (016)
> although constrained nowadays by government rules. (017)
and before that by societal rules. (018)
> Although they are typically
> defined in two dimensions only, their third dimension is recognized and
> constrained by government rules (as you describe below). (019)
It appears that you are referring to plots of land here, not "two
dimensional area's in physical reality". (020)
> This is related to the concept of 'surface'. A surface can have a
> roughness,
> a color, a hardness, a temperature, a strength, etc. I think that it can't
> have such properties when it would be only two dimensional. (021)
One could certainly define such, e.g., the lat/long of its centroid. (022)
> We are probably
> influenced by the abstract mathematical concept of dimensions.
> In practical physics, every physical point has a size that is non zero,
> although nearly infinitesimal. (023)
What do you mean by "physical point"? (024)
>> By fiat, the governments of countries lay claim to the mineral
>> rights beneath their areas. In principle, they could claim rights
>> down to the center of the earth. But in practice, the technology
>> can only mine a few km. beneath the surface. (025)
>> When air travel became possible, national governments laid claim
>> to the air space above them, but smaller governments did not.
>> But nobody laid claim to the regions above the atmosphere.
>> Those are more distinctions by fiat. (026)
>> In summary, I recommend that any ontology for any subdivision
>> of the earth should specify the surface area S and the intended
>> role R for that area. (027)
> [AvR] In some cases (e.g. mines, reservoirs) the subdivision of the earth
> requires an explicit third dimension. (028)
Agreed. (029)
> And some, such as lakes and mountains, don't need a role. (030)
Huh? Wouldn't a lake/mountain have the roles of being part of some
enitity's territory and some (other) entity's property? (031)
>> Then anything else that may be associated with the pair (S,R),
>> such as the land, air, water, people, buildings, governments,
>> should be specified as the X associated with the area S as
>> considered in the role R. (032)
>> John (033)
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