Need help with gravity.

[Somnio-alibi]

I know that gravity depends upon mass but what if the mass was spread out? For instance, Jupiter has a great amount of mass and therefore very powerful gravity but what if you flattened Jupiter into a great ring around the sun? Would any part of that ring retain the full gravitational force of the planet equal to when the planet was one round ball? Or would the spread out mass greatly affect the gravitational pull of the ring?

 

I don’t know a lot about gravity so I have no idea. Need some help if you can. Thanks!!!

[EvoN1020v]

Gravity pulls [math]9.81 m/s^2[/math] on all matters ON EARTH. Depending on their shape, their acceleration can be slower due to air resistance. Gravity on different planets differ from Earth's. Does that answer your question?

[theCPE]

Mass creates space-time curvature which results in 'gravity'. The strength of the gravity is proportional to the inverse square law. Meaning, the further away an object is from the center of mass the weaker effects it feels from the gravity.

 

If the same mass is distributed into a ring the center of mass is still in the center of the ring and thus the direction the gravitational force pulls you toward. However, the radius (distance) from the center of mass will most likely be changed and therefore the gravity will feel a different strength. If the radius from the center of gravity is kept the same it would be unchanged.

 

Like with black holes and collapsing stars. The only reason a black hole has "stronger" gravity than the star it was created from is because the radius to 'surface' shrinks drastically. If our sun collapsed into a black hole we wouldn't feel any change in gravity.

[Klaynos]

No, no point of the ring would have the same gravitational attraction as the planet.

 

EvoN1020v, this is not about gravity on earth.

 

You work out the gravity from a system by analysing the mass distribution, the easiest way to do this is to use Gauss's law for gravity:

 

http://en.wikipedia.org/wiki/Gauss's_law#Application_to_Gravity

 

So if there is only one mass you are considering, when you are close to it the shape is important.

[theCPE]

True, the distribution of center of mass matters as well as radius, my mistake!

[Somnio-alibi]

First I would like to thank EvoN1020v, theCPE, and Klaynos for your responses. I’m afraid some of the answers went over my head. Let me start by explaining why I want to know. I’m writing a fantasy novel with a little science fiction thrown in. I’m toying with the idea of making a world that is like a great ring around a sun. I like this idea because one it’s different from the traditional round planet and two it would give me more than enough land to play with in my world. BUT, I need the gravity to be the same as on earth (or at least comparable). If this is completely implausible I might scratch the idea. If someone landing on this land(ring planet maybe) gets immediately sucked off it towards the center of the ring, which would be towards the sun, then of course that would not be good. My major question is: is it possible for me to finagle this scenario into the semi plausible area or would gravity either crush or fling all the inhabitants off the ring to an early death? Thanks again.

[foodchain]

First I would like to thank EvoN1020v, theCPE, and Klaynos for your responses. I’m afraid some of the answers went over my head. Let me start by explaining why I want to know. I’m writing a fantasy novel with a little science fiction thrown in. I’m toying with the idea of making a world that is like a great ring around a sun. I like this idea because one it’s different from the traditional round planet and two it would give me more than enough land to play with in my world. BUT, I need the gravity to be the same as on earth (or at least comparable). If this is completely implausible I might scratch the idea. If someone landing on this land(ring planet maybe) gets immediately sucked off it towards the center of the ring, which would be towards the sun, then of course that would not be good. My major question is: is it possible for me to finagle this scenario into the semi plausible area or would gravity either crush or fling all the inhabitants off the ring to an early death? Thanks again.

 

I would look at rings around other planets. I mean they have been existing for sometime without simply falling apart in an instant, relative to our observations I guess. Plus if its a sci-fi novel it does not always need to be perfectly honest. I mean most spaceships in sci-fi such as star trek always have some perfect energy source for instance to power the ship.

[theCPE]

you can always make the ring spin to create artificial gravity, assuming the inner surface is where the people/stuff live.

[Somnio-alibi]

I would look at rings around other planets. I mean they have been existing for sometime without simply falling apart in an instant, relative to our observations I guess. Plus if its a sci-fi novel it does not always need to be perfectly honest. I mean most spaceships in sci-fi such as star trek always have some perfect energy source for instance to power the ship.

 

Ya, I hear what you’re saying but I don’t want it to be obviously ridiculous. If it’s half possible then I will keep but, like I said, if it’s just scientifically irreconcilable then I have a problem.

[Somnio-alibi]

you can always make the ring spin to create artificial gravity, assuming the inner surface is where the people/stuff live.

 

That's a good idea. I know some space stations operate like that. I know there will be a side of it that will never get any sun. I planed to get around the day and night thing with a cloud ring between the sun and the habited land. The cloud ring would be vertically thicker around half the circle allowing for night. As day turns into night the sun would appear to be shutting it’s eye. Of course the sun would always be in the same position.

[Klaynos]

you could make the gravity on the outside of the ring the same as the earth, but if you moved around the the ring to be on the inside, the gravity would change, in a non-linear manor, and on the inside of the ring the gravity from the ring would be 0. So because there is a star in the middle you'd fall off... If it's spinning you could create an artificial effect that would seem like gravity on the inner edge, but again this would not be constant as you moved from inside to outside.

[Somnio-alibi]

you could make the gravity on the outside of the ring the same as the earth, but if you moved around the the ring to be on the inside, the gravity would change, in a non-linear manor, and on the inside of the ring the gravity from the ring would be 0. So because there is a star in the middle you'd fall off... If it's spinning you could create an artificial effect that would seem like gravity on the inner edge, but again this would not be constant as you moved from inside to outside.

 

OK…let me try and get what you are saying. The ring will be spinning so lets say there are four sides to the ring (like the ring around Saturn: the inside side (facing the sun), the flat top of the ring, the outside side(dark side), and the flat lower side (facing down). How would gravity work on these four sides? Also…the idea that you could fall off the world is terribly fascinating. I would like to hear more about this possibility. If one falls off the world, where do they fall?

[Klaynos]

I'll do the 4 sides tomorrow evening if no one else has yet.

 

But falling off was for a non spinning ring, and it'd be on the inner edge and you'd fall towards the sun

[Somnio-alibi]

I would also like to add, if I understand your original reply, If the ring is not spinning and there is sufficient gravity on the top flat side, and by moving to the outer rim one could fall off the world, this scenario would be the most desirable. Lots of possibilities in a fantasy world.

[Somnio-alibi]

I'll do the 4 sides tomorrow evening if no one else has yet.

 

But falling off was for a non spinning ring, and it'd be on the inner edge and you'd fall towards the sun

 

Thanks, I appreciate it.

[theCPE]

With a star in the center of the ring you are going to have a hard time keeping objects on the inside of the ring. The gravity from the star would easily keep objects on the outside side of the ring, unless of course this ring you are talking about has some ridiculus radius. And then if you make the ring rotate so that artificial gravity is created for the inner side of the ring you are going to sling anything off the outer side.....unless of course the thickness from the inner side to outer side is ridiculus.

 

But since this is a sci-fi book/story you really don't have to worry about the details so much. I would say rotate the ring and put the stuff on the inside and copy/paste some pictures of the rings from Halo and I'd say your book is set:)

[Somnio-alibi]

With a star in the center of the ring you are going to have a hard time keeping objects on the inside of the ring. The gravity from the star would easily keep objects on the outside side of the ring, unless of course this ring you are talking about has some ridiculus radius. And then if you make the ring rotate so that artificial gravity is created for the inner side of the ring you are going to sling anything off the outer side.....unless of course the thickness from the inner side to outer side is ridiculus.

 

But since this is a sci-fi book/story you really don't have to worry about the details so much. I would say rotate the ring and put the stuff on the inside and copy/paste some pictures of the rings from Halo and I'd say your book is set:)

 

Thanks for the feed back. The book is already written but I keep adding ideas to it. The original world was round like Earth but had a greater diameter. To get around the gravity problem I simply stated that there were great hollow spaces within the Earth. This became a convenient setup when I put, on the East and West pole, two massive geysers at each end. The planets inner core caused the water within the Earth to heat up and spew endlessly from both sides. This force is great enough to send the water out of our atmosphere and create a ring of liquid water around the Earth. The circling would only be temporary due to Earths gravitational pull so the water flows down near the East and West poles, only to again be thrust back up into space by the perpetual geysers. This endless cycle allowed for a thin atmosphere to follow around the ring therefore allowing ships to sail out into space and return on the other side of the world. This was my first idea and I really like the liquid ring idea but I’m experimenting with other ideas.

[J.C.MacSwell]

Thanks for the feed back. The book is already written but I keep adding ideas to it. The original world was round like Earth but had a greater diameter. To get around the gravity problem I simply stated that there were great hollow spaces within the Earth. This became a convenient setup when I put, on the East and West pole, two massive geysers at each end. The planets inner core caused the water within the Earth to heat up and spew endlessly from both sides. This force is great enough to send the water out of our atmosphere and create a ring of liquid water around the Earth. The circling would only be temporary due to Earths gravitational pull so the water flows down near the East and West poles, only to again be thrust back up into space by the perpetual geysers. This endless cycle allowed for a thin atmosphere to follow around the ring therefore allowing ships to sail out into space and return on the other side of the world. This was my first idea and I really like the liquid ring idea but I’m experimenting with other ideas.

 

This makes me think it has some kind of multidimensional quantum spin:D

[kindadevil66]

i agree with food chain on this and a science fiction book does not need exact gravatational pulls and what not but that is good i did not no that nomber but yea good luck on the book