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View Full Version : Why Always Round...Spherical.....Circular...Cyclic even!



Eric Vaxxine
2010-Nov-30, 12:40 AM
When you look into the universe.....stars and planets are always 'round'!

If you delve inside the molecules of your laptop or those of
your lunch or those your mother-in-law...
you'll also find that they are built of molecules, round.

Is there any possibility of our universe offering up a physical
un-round object, outside of 'gravity - rounded' norm?

Or is our universe obviously commited..... to go around?

Bynaus
2010-Nov-30, 07:51 AM
The surfaces of objects are (essentially) equipotentials: attempts of matter to achieve a state of equilibrium. As gravity is a 3d, unidirectional force, the only logic shape for a body dominated by gravity is a sphere. Fast rotation can lead to elongated or oblate objects (like Altair, the star, or Haumea, the dwarf planet), but again, these are equipotential surfaces. External forces (like solar wind, or high UV flux) can transform equipotential surfaces into teardrop shapes (like comet tails, or cloudlets in a giant molecular cloud under the influence of a high-UV nearby star).

If you want ring- or cylinder-shaped objects, you have to find conditions where the relevant forces form equipotential surfaces of this shape. I guess that this can only be achieved on objects dominated rather by chemical binding forces than by gravity.

Jens
2010-Nov-30, 09:11 AM
And I think the general principle works outside of gravity. For example, water drops are spherical because of surface tension.

Strange
2010-Nov-30, 09:38 AM
Crystals come in all sorts of exotic shapes. I suppose it is conceivable that there could be an asteroid consisting of a small number of individual crystals, which would be very non-round.

Also, on a different scale, electron orbitals come in all sorts of shapes including "donuts" and "dumbbells". Of course, this is still about minimum energy configurations

Hungry4info
2010-Nov-30, 12:56 PM
It's an efficient shape as well -- storing the most volume into the least amout of surface area.

AndreasJ
2010-Nov-30, 01:35 PM
If you delve inside the molecules of your laptop or those of
your lunch or those your mother-in-law...
you'll also find that they are built of molecules, round.
Molecules aren' t always round. This is particularly true of big biomolecules as may be found in your lunch or mother in law (a DNA strand is about as unround as anyone can ask for), but also of very simple molecules like O2, which is very distinctly non-spherical.

Are you possibly thinking of atoms?

Jeff Root
2010-Nov-30, 05:03 PM
Molecules are almost never round.

Atoms generally are only sorta round.

Fundamental particles don't have shapes.

-- Jeff, in Minneapolis

Paul Beardsley
2010-Nov-30, 05:55 PM
The reason so many things are cyclic is because if they weren't, they wouldn't come round again, so you'd only see them once. Instead of referring to past summers, we'd refer to that warm period ages ago. Instead of referring to Christmas, we'd refer to that time when everyone spontaneously bought everyone else a present and stuck a tree in their lounge for some reason. Young ladies would endure an uncomfortable few days, then say, "Well thank goodness that's over!"

neilzero
2010-Dec-01, 07:39 AM
The largest asteroids and moons are approximately spherical or spheroid, but small and medium sizes come in a wide variety of shapes. Some orbits are quite elliptical, rather than round. Small objects pass though the solar system, at about 100 kilometers per second, to return billions of years in the future or never.
Likely a large object will just pass though, perturbing the orbits of the planets, but we have not observed and confirmed any such passage. Neil

Eric Vaxxine
2010-Dec-06, 12:38 AM
Great knowledgeable replies, thank you all.

"Spherical or spheroid....' ..elliptical..' " .....to quote 'neilzero'....

I suppose it would take some new threads to ask......
'what kind of worlds could have
trianglular or trapezeoid gravity by default?'

'What kind of worlds could have
a square or rectangular gravity by default'

If this thread ends here....I understand.
(I am a guitarist by trade, not anyone learned in science or maths)

Nowhere Man
2010-Dec-06, 04:12 AM
The answer to both questions is, "None in this universe." For more fun look in Google Images for Escher double planetoid.

Fred

dgavin
2010-Dec-09, 02:06 AM
Great knowledgeable replies, thank you all.

"Spherical or spheroid....' ..elliptical..' " .....to quote 'neilzero'....

I suppose it would take some new threads to ask......
'what kind of worlds could have
trianglular or trapezeoid gravity by default?'

'What kind of worlds could have
a square or rectangular gravity by default'

If this thread ends here....I understand.
(I am a guitarist by trade, not anyone learned in science or maths)

You'll find all these shapes applied to various moons in the Xanth novels by Piers Anthony. However Xanth is a fictional universe that operates on Pun's instead of Physics.