Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Atomic-S on 14/04/2006 05:52:13
-
Were the Earth flat, methinks it could be bigger.
As a planet spins, it bulged equatorially. If it spins fast enough, the effective gravity at the equator reduces because of centrifugal effects plus greater distance from the center, and that elsewhere also reduces because the planet becomes thinner. This suggests the possibility that somewhere a planet having a surface area comparable to that of the Sun, but an effective surface gravity comparable to that of the Earth, could exist if it were spun into a disk-like shape.
There must be some references someplace on this subject. Does anyone know any?
-
1) where did this planet obtain so much rotational energy?
2)I suspect such a planet would have torn itself apart, and would no longer be a plane.
3)With so much surface area, and so little mass, would it not have the effect of being a highly effective solar sail, being pushed out of the solar system by the force of the solar wind acting upon it.
George
-
I imagine living near the center of this disk would be quite dull compared with living near the edge!?
Subduction causes orogeny.
-
If the world is flat then the sun is going around it and if you sail too far you will fall off. I know I heard this somewhere before but I just can't remember where. [:D][}:)][:D]
What you do speaks so loudly that I cannot hear what you say.
-
I think what you mean is a very oblate (flattened) spheroid, I see no reason why this wouldn't work, up to a point. I am not sure that it would work if there was a largeish moon in orbit, as the tides would slow it down so it would become more like a sphere again.
It would have an interesting effect on the climate, as most of your planet is essentially polar, so you are either going to get very weak sunlight, or 6 month's of day and night. If the planet's axis was tilted like earth's then you will have summers and winters where half your massive planet is very hot and the other half very cold, this will produce some serious winds, especially when coupled with the amount of angular momentum you have in the system, you are going to get some serious storms!!
I think I will stick to this boring old ball if it is all the same with you.
-
An amusing "Greg Bear" type planetary enginerering idea and an interesting extension of discworld
Learn, create, test and tell
evolution rules in all things
God says so!
-
quote:
1) where did this planet obtain so much rotational energy?
Well, where did any planet obtain its rotational energy?
quote:
2)I suspect such a planet would have torn itself apart, and would no longer be a plane.
That is one of the questions to be answered. Up to a point, of course, it won't.
quote:
3)With so much surface area, and so little mass, would it not have the effect of being a highly effective solar sail, being pushed out of the solar system by the force of the solar wind acting upon it.
The mass of such a planet is not necessarily negligible. If it were 10^6 miles in diameter and 1 mile thick, made of the kind of stuff the Earth is, that is still quite a hefty load to be moved by the solar wind.
quote:
I imagine living near the center of this disk would be quite dull compared with living near the edge!?
Not necessarily. Assuming the system is stable, the surface is everywhere coincident with an equipotential surface. That does not necessarily mean, of course, that the observed acceleration of gravity by an inhabitant would be everywhere the same, but it would be everywhere perpendicular to the surface. The coriolis effect caused by the spinning is not, I think, necessarily enormous (so that you could not walk along without becoming dizzy); that depends on the particular parameters involved. If the planet is quite large, its angular velocity would probably be small. we would have to get into details as to exactly how the magnitude of observed gravitation varied from place to place. that too depends on exact circumstances. One way in which things at the center might be highly interesting is if the magnitude of surface gravity there turned out to be a complex number, a situation which would indicate that there would be no surface there, l.e., the body would form into an oblate doughnut rather than a disk. Whether this is dynamically stable without the injection of forces other than gravitation ans spinning, I do not know.
quote:
If the world is flat then the sun is going around it and if you sail too far you will fall off. I know I heard this somewhere before but I just can't remember where
No, because this disk is not quite a strict disk (very oblate spheroid, as daveshorts correctly pointed out). If it is covered with ocean, a sailor would always observe gravity to act at right angles to the surface, and would never sail off. That assumes, of course, that the velocity of the periphery (equator) is somewhat less than orbital velocity at that point. Now if it equals orbital velocity, things get interesting. If it exceeds orbital velocity, the sailor would indeed fly off, but then again, so would the ocean and the system would be unstable.
quote:
I think what you mean is a very oblate (flattened) spheroid, I see no reason why this wouldn't work, up to a point. I am not sure that it would work if there was a largeish moon in orbit, as the tides would slow it down so it would become more like a sphere again.
Well, you may be right but the proces might take virtually forever, and even then might slow it only to a certain limiting value that is never gone below as long as the moon remains in orbit. Also, what if the moon's orbit is polar rather than equatorial?
quote:
It would have an interesting effect on the climate, as most of your planet is essentially polar, so you are either going to get very weak sunlight, or 6 month's of day and night. If the planet's axis was tilted like earth's then you will have summers and winters where half your massive planet is very hot and the other half very cold, this will produce some serious winds, especially when coupled with the amount of angular momentum you have in the system, you are going to get some serious storms!!
That could be a problem; then again, why do we necessarily have to assume that the planet's environment is like that of the earth? Maybe it could be in a much closer orbit to a star (not necessarily of the same brilliancy as the Sun), which means that the duration of the summer/winter cycle would be much shorter. How does the percentage of the surface that is liquid affect these dynamics? What about atmospheric composition and density? Maybe it is located in a star cluster where it receives significant radiation from more than one direction. Many possible variables to consider.