Gravity: Earth-sized platinum sphere with 3 meter empty center - behavior

[ndvcxk]

of loose object in the center. This object is now surrounded by mass, will it hover exactly in the center of the hole, is there no gravity there ? If it is flexible, will it be expanded if it is expandable. How does one calculate this?

(For realism, assume symetrical 2 meter channels from the surface of the giant sphere by which the object was lifted down into the center.

Thx, from physics newbie.

 

[ChrisAndre]

Yes, there will be gravity. However, not what you feel as that force that holds you on the floor. It will be pulled on all sides and stretched because of this. This happens because there is relatively equal mass every direction you look as compared to other directions, and so you feel a force in every direction. However, realistically it will not float. Two reasons: gravity from other objects outside the sphere (assuming you've placed it in our universe,) and (if you have it by itself, no other objects in "it's" universe) that nothing can be exactly in the center, and thus by the theory of gravity more force(very very very very minute) will be felt on one side than the other because of this offset and because difference in force equals movement, it will ever so slowly move closer to the edge of the compartment. If you find a way to place it exactly in the center, it will do nothing but expand, if expandable.

As far as calculations go I would think it would involve dividing the object up many times and doing calculations for each division.

 

[Dale]

If you find a way to place it exactly in the center, it will do nothing but expand, if expandable.

I don't think there are any tidal forces from the sphere.

 

[Janus]

I don't think there are any tidal forces from the sphere.

Right, because tidal forces require a gravitational differential, and due to the Newton's shell theorem, the net gravitational force will be zero at all points of the hollow.

 

[Lsos]

It will be a situation of microgravity just like when orbiting the Earth in a spaceship. Sure there'll be some >0 force in some direction from something, but for all intents and purposes, a person in this empty center will be free-floating.

 

[ChrisAndre]

Thanks for the correction. I understand now.

 

[ndvcxk]

Thx for responding guys,
Let's say there were symmetrical tunnels leading to the hole at the center of the sphere, such
that you could slide down, finally coming to rest at center (after zipping into the opposite direction)

Now, as you hang in the center, the two masses should be exerting opposite effects, but I take it the consensus is that the gravity waves are compensating, i.e. each atom in your body is separately pulled and pushed, meaning a smooth float..right..? thx

 

[Lsos]

Pulled. But yes, you would float.

 

[Subductionzon]

Pulled. But yes, you would float.

Pulled, how? Janus nailed it when he said Newton's shell theorem solves this problem. All of the gravitational forces cancel on the inside of a shell. Your answer seems to indicate you would be pulled to opposite sides at the same time. A body would only feel "pulled" if the forces were different on it at different points. Everywhere you are on the inside of a shell the forces all add up to zero. There is no place in it that is pulled to one side more than the other.

 

[Lsos]

I was just trying to specify that gravity pulls, not pushes, in response to the poster above me.