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Melamed
2009-Jun-01, 01:20 AM
Just for personal pleasure I've decide to delve into the works of einstein such as space-time and other theories that try to explain everything. I believe that if I truly want to understand it I'm going to have to figure it out by making my own conclusions on information that I find or have hypothesized.

Please someone answer these questions for me, as I have have no idea where to look for the answers (tried google but it didn't help). They're pretty important to what I'm looking at now and I do not have the theoretical knowlege or the means to observe this information.

First I need to know the mass and density of planets, stars or other celestial bodies (as many and as exact as possible). I also will need the planet's (or whatever) radius to their surface, and radius to the edge of their field of gravity.

One other thing. You know that experiment where you use liquids of different density, put them in a container and let them separate? The heaviest/ most dense liquid end up on the bottom. You could use more than two liquids too and they will always arrange themselves most dense to least dense with the most dense liquid closest to the source of gravity and a clear partition between each liquid that is perpendicular to the force of gravity.
My question is how would the liquids arrange themselves if they were in space far from the gravitational pull of any celestial mass. My prediction is that the heaviest particle will eventually be forced into the center of the container forming a sphere. The other liquids will form layers around the sphere with the next most dense liquid as the first layer around the original sphere of the most dense liquid. the least dense material will evenly distribute itself between the surface of the sphere and the walls of the container, even despite the shape of the container. (note that this is not in chronological order but merely a description of how the substances will be arranged once they have been given enough time)

My reasoning is that since the most dense substance ( call this "L1" for liquid 1) will have the largest and strongest gravitational pull. All of the particles of this liquid have a stronger attraction than any other two particles to eachother. The liquid with the second highest density ("L2") will be first attracted to L1, meaning it will move as close to it as possible, closer than any other particle will. Since the third highest attraction after L1=>itself and L2=>L1 is L2=>itself, all of the L2 particles will form a layer together evenly distribute surrounding L1. Other liquids in the container will successively mimic the behaviour of the first two liquids, forming more layers.
The reason I came to the conclusion the the particles would form a sphere is that in our example on earth the partitions between the substances were perpendicular to the force of gravity. I bet that if you made a container that was as wide as the earth and set it down or hung it by string from the moon whatever, the partition would be curved in a way that if you took the perpendicular to a tangent of this curve and drew it from the point of intersection with the curve, it would point straight to the center of the earth and the length each of these tangent's perdicular from the curve to the earth will be equal(i.e. parallel to the force of gravity.) Thus the ideal arrangement of the liquids in our container would be a sphere with the source of the strongest gravity, which is L1, at its center. Now the next layer can be formed and the properties of the partition in the example on earth is identical to the ones in our container which is unaffected by outside gravitation.

I am no physics major, in fact I dropped all sciences in grade 11, so I have no idea if this is the case or not. For all I know the liquids don't move at all when they are not affected by the gravity. If this is the case it supports my thoughts, so please someone confirm this.

grav
2009-Jun-01, 01:52 AM
Welcome, Melamed. That is the way I would figure the densities of the liquids would eventually distribute themselves also, even according to their own gravity in free space. Here (http://www.smartconversion.com/otherInfo/Density_of_planets_and_the_Sun.aspx) is a link for the densities of the planets and sun.

01101001
2009-Jun-01, 02:03 AM
You know that experiment where you use liquids of different density, put them in a container and let them separate?

Immiscible liquids, I presume.

I'd expect different results depending on at least one force still in operation in zero-G: surface tension. The minimal energy state might be different from what you expect in some cases. I don't know for sure though. I bet someone does.

Ken G
2009-Jun-01, 02:03 AM
First I need to know the mass and density of planets, stars or other celestial bodies (as many and as exact as possible). I also will need the planet's (or whatever) radius to their surface, and radius to the edge of their field of gravity.The density of rock is always something like 4 g/cc, and gas is usually about 1 g/cc. If you want better accuracy, use Google, but note that the density varies from planet to planet. Same with the radius, but a terrestrial planet is often about 10,000 km in diameter, and a gas giant is often 10 times that. These are rough numbers, because the values vary a lot, even just in our own solar system. There is no "edge of their field of gravity", gravity just gradually weakens in proportion to one over the distance squared. (Like an old soldier, it just "fades away". That is why it is incorrect to imagine that Newtonian gravity does not extend into space where astronauts are orbiting a planet.)


My question is how would the liquids arrange themselves if they were in space far from the gravitational pull of any celestial mass. My prediction is that the heaviest particle will eventually be forced into the center of the container forming a sphere.That is correct in principle if gravity is the only thing going on, and the system reaches zero temperature. In practice the self-gravity of a bottle of fluid is probably too small to ever witness this effect, there is surface tension, and the presence of a finite temperature might mess things up. So there's the problem of timescale, maybe it wouldn't even happen in the age of the universe today, I don't know. And there is the problem that there may be lower energy configurations if the fluids are mixed, but I don't think so-- I think the configuration you mention would be the lowest energy one. If so, then in an idealized case where you have an arbitrary amount of time, and the system is allowed to cool, then yes, that is what would happen. You might have to shake the system up though-- sometimes you can have local energy minima that are not the global minimum but serve as stable configurations in the absence of enough stirring (hence the point about the need for the fluids to be immiscible.) I think the bottom line is, you'd better have a very large (say, planet-sized) container, so that the gravity is pretty strong.

Jens
2009-Jun-01, 02:06 AM
That is correct in principle, but in practice the self-gravity of a bottle of fluid is probably too small to ever witness this effect.

Wouldn't that depend on the size of the bottle? In normal practice, yes, but suppose you had a really, really big bottle?

PraedSt
2009-Jun-01, 02:08 AM
First I need to know the mass and density of planets, stars or other celestial bodies (as many and as exact as possible). I also will need the planet's (or whatever) radius to their surface, and radius to the edge of their field of gravity.
Everything but the last will be in Wikipedia (http://en.wikipedia.org/wiki/Earth). You could start there.

Welcome to BAUT.

Nowhere Man
2009-Jun-01, 02:13 AM
There are also places called "libraries." Any well-appointed town (in the US, at least) will have several. Find the physics section, and ask the people who work there for guidance. Tell them you want some beginners' physics texts.

Fred

grav
2009-Jun-01, 02:30 AM
Here (http://www.smartconversion.com/otherInfo/Density_of_planets_and_the_Sun.aspx) is a link for the densities of the planets and sun.Oh, you can also click on the list to the left of that page I linked to to get the masses, volumes, surface areas, and temperatures.

01101001
2009-Jun-01, 02:38 AM
I bet someone does.

SP-401 Skylab, Classroom in Space, Chapter 12 (http://history.nasa.gov/SP-401/ch12.htm)

It's a light treatment, but I'm sure the scholoarly papers exist.


A number of fluid-mechanics experiments were performed in Skylab to demonstrate and to evaluate the behavior of liquids under conditions where surface tension forces dominated. In certain cases, phenomena were demonstrated that are not possible on Earth; in others a comparison between the phenomena in space and on Earth was possible.

A knowledge of zero-gravity fluid mechanics is essential to the design of any fluid system that operates in space, from rockets with liquid propellants to the water used in a life-support system. In the future, space may become the best place for processing of materials and pharmaceuticals, thus eliminating detrimental convection and sedimentation effects caused by gravity, and permitting containerless handling of fluids where contamination from the container occurs. In order to perform such processes, the basic fluid phenomena must be understood. Even Earth-based phenomena, such as the falling raindrop mentioned above, can be studied in a more basic form when the effect of gravity is eliminated.

Jeff Root
2009-Jun-01, 02:46 AM
Just for personal pleasure I've decide to delve into the works of einstein
such as space-time and other theories that try to explain everything.
Have you been reading my recent posts???

Hello, Melamed!



First I need to know the mass and density of planets, stars or other
celestial bodies (as many and as exact as possible). I also will need
the planet's (or whatever) radius to their surface, and radius to the
edge of their field of gravity.
There is no edge to any field of gravity. The strength of a gravity
field falls off as the square of the distance from the source. The
mass-energy of your body gravitationally attracts Mars by a very
tiny amount. It attracts Neptune by a much tinier amount. And it
attracts the star Alpha Centauri by a much, much tinier amount than
that. In principle, the force only becomes zero at infinite distance.
However, for bodies moving through space, such as planets and
stars, there is a distance beyond which their gravity becomes less
important than the gravity of other bodies nearby. That is called
the "Hill sphere", which you can look up.

For equatorial diameter, mass, and mean density of planets in our
Solar System, you can look here (http://www.freemars.org/jeff/planets/planets5.htm). You can click on the green links
to the planets for more info, including things like mean diameter,
polar radius, and oblateness, if you want them.

When you see diameters given for stars like the Sun, they refer to
the diameter at the top of the photosphere, which is where most of
the light comes from that we can see. However, there is not a big,
sudden difference in density above and below that level. The density
drops very gradually from very high density in a star's core, to very
low density in the photosphere (less dense than Earth's atmosphere),
to extremely low density in the corona. Overall, a star like the Sun
is very low density. Only 1.41 times the density of water, in the case
of the Sun, as compared to 5.52 times the density of water for the
Earth, which is the densest planet, slightly denser than Mercury.



My question is how would the liquids arrange themselves if they were
in space far from the gravitational pull of any celestial mass.
They would most likely either freeze or vaporize, or both. Ever hear
of "freeze-drying"? That's what happens. But it depends on the
liquids and the ambient radiation, which determines their temperature.



My prediction is that the heaviest particle will eventually be forced
into the center of the container forming a sphere. The other liquids
will form layers around the sphere with the next most dense liquid as
the first layer around the original sphere of the most dense liquid. the
least dense material will evenly distribute itself between the surface
of the sphere and the walls of the container, even despite the shape
of the container. (note that this is not in chronological order but merely
a description of how the substances will be arranged once they have
been given enough time)
Gravity is an extremely weak force. The mass of liquid would need to
be very large for self-gravity to cause differentiation into layers. It
would need to be a glob comparable in size to some of the larger
asteroids. Several hundred miles in diameter.

Every liquid has cohesiveness. Electric forces between the atoms and
molecules hold them in contact with each other. The most obvious
and familiar expression of this is surface tension. It causes a blob of
water in a spacecraft orbiting Earth to form a ball. Experiments have
been performed in orbit combining and separating various liquids. I saw
a video of one that was done aboard Skylab in the 1970's. A blob of
two liquids was spun around until they separated from each other
and flew apart in opposite directions.

We can get into more of the specifics of your ideas in later posts.

-- Jeff, in Minneapolis

Ken G
2009-Jun-01, 05:40 AM
Wouldn't that depend on the size of the bottle? In normal practice, yes, but suppose you had a really, really big bottle?Yes, I think it would need to be very big.