Re: Question

From: Paul Draper (pdraper_at_yahoo.com)
Date: 10/28/04 

Date: 28 Oct 2004 08:39:06 -0700

Deborah <deborah@invalid> wrote in message news:<t571o01aql0m3141ff2tk7dt45eeub28vj@4ax.com>...
> On 28 Oct 2004 06:58:19 GMT, pumaracing@aol.comNoEmails (Dave Baker)
> wrote:
>
> >>Subject: Question
> >>From: Deborah deborah@invalid
> >>Date: 28/10/04 07:48 GMT Daylight Time
> >>Message-id: <4751o05fimkrb1emtomtosr9goh8nt6eu2@4ax.com>
> >>
> >>Pardon me for butting in - I'm just visiting temporarily. The lunar
> >>eclipse tonight got me wondering about something that I don't know the
> >>answer to. It's going to sound pretty elementary to you, I'm sure,
> >>but here is my question:
> >>
> >>Why are almost all of the bodies in the universe - whether we're
> >>talking about stars, planets, moons or the most basic building blocks
> >>of matter at the atomic level - spherical in shape?
> >
> >Gravity
>
> Can you elaborate a little? How does that work? I mean, gravity is
> an internal force of each body, right? So basically, to explain the
> spherical shape of these bodies in terms of gravity amounts to saying
> that it is their own internal nature to be spherical?
>
> Why is it their own internal nature to be spherical, or do the
> questions just stop there?
>
> It just is?
>
> Deborah

I'd think of it as energy optimization. Some forces can be thought of
as giving a form of energy (e.g. gravitational potential energy) to an
object or a conglomeration of objects, and systems of objects tend to
settle to states with lower energy. In the case of a conglomeration of
loose particles, all subject to each other's gravitational pull,
there's a little mathematical demonstration that shows that the
minimum energy of that set will be in the form of a sphere. Much the
same way you can prove mathematically that the 2-dimensional shape
with the minimum perimeter for a given area is a circle. As anecdotal
evidence, consider some shapes with area 1 sq.in.: the perimeter of a
1/2"x2" rectangle is 5", the perimeter of a 1"x1" square is 4", the
perimeter of a circle with area 1 sq in is 3.54491".

(This kind of relation has LOTS of implications, by the way. It's the
reason why water drops are round, it's the reason why the tallest &
thinnest humans are at equatorial climes, it's the reason why
spreading water thinly over a surface causes it to dry faster, and the
reason your lungs and intestines have villi. If you're interested,
there's an EXCELLENT article in last month's Physics Today at your
library that talks about scaling laws in living organisms.)

Quantcast