Gravity of celestial objects like earth.

[Bodhisattva]

Hello.
I am wondering about this:

The gravity of a celestial body like Earth is working towards the center of the mass.
So if you are in the center of the earth, gravity pulls from the center, towards the surface?
So is there a very dense sphere that consists of iron in the center of our planet or is there a void?

 

[BradtheRad]

We would fall toward the center of the earth, even though we weigh the most at the surface. We would be weightless in the very center.

Geodynamicists (geophysicists?) believe the core of the earth is molten iron. I think I've heard it will never cool. It is kept molten by the heating effect of intense eddy currents, and heat due to continuous circulation under the enormous pressure.

 

[Bodhisattva]

I heard this official hypothesis before. But where is the pressure coming from if the force of gravity is directed away from the center of the earth?
This is the part I don't quite get.

 

[BradtheRad]

I heard this official hypothesis before. But where is the pressure coming from if the force of gravity is directed away from the center of the earth?
This is the part I don't quite get.

That's a good one you're asking. Every so often we hear a question which makes us wonder if everything we know is false.

Yes, if it is zero gravity at the center of the earth, then how can it be under immense pressure?

Hmmm...

I believe the line of reasoning is that a body is pulled toward the greater concentration of mass. If there is greater mass to your right side, and less mass to your left, then gravity pulls you toward the right.

That is why you would fall toward the center. It is the spot where there would be an equal balance of mass all around you.

It still seems like a paradoxical situation, just the same. Immense pressure at the center of the earth, yet also zero gravity. Every object on earth feels a pull toward earth's center, except whatever is already at its center.

 

[Bodhisattva]

So at the center of a black hole there is an area of an undetermined size where the gravity is approaching zero and particles that are pushed to the border of the area will not approach the center of the area because they are attracted towards a more dense shell that surrounds this area?

So the center of mass of a celestial body cannot be the center of peak density? So a 'hollow' sphere may be, where the increase in density is about 3/4 of the way between the center and the outer surface? I will need to do some math to figure out where that density horizon is.
There may also be a greater void in the center that would make my calculations useless.

So our Earth may be filled with hydrogen in the center or there may be Hell with souls of the sinners, but less likely there is a peak of density at the center. :-D

Maybe this is where the strange hypothesis that the Moon is hollow coming from.

 

[BradtheRad]

Even near the earth's center, the denser objects will tend to sink below less dense objects. Perhaps they do not sink as fast, since gravity is less.

Anyway I've never heard that a celestial body can be hollow at the center, in normal circumstances. The force of gravity attracts shapeless masses of gas and particles, to gel together tightly into a spherical shape.

Seems I needed a refresher about what's at the core of the earth. Solid metal according to diagrams like this (copied off the internet):

And I would not expect to find souls at the center of the earth, regardless of the report (in the Weekly World tabloid) that voices could be heard when researchers dropped a microphone down a ten-mile deep shaft. :^)

 

[Bodhisattva]

This is an official hypothesis, that the core of the Earth is dense iron. Apparently studies of how axis of rotation of bodies like Earth and Moon fluctuate proves proves that certain inertia characteristics can only exist if their composition is as it is described.

I am just wondering if there is a space in the center of the planet that maybe is one meter in diameter that is not as dense.

If there are souls of sinners inside the Earth than a Deity should perhaps sit on a cloud, somewhere in the upper layers of atmosphere.
That dude with a long gray beard.

 

[BradtheRad]

Since Earth has a magnetic field, that becomes a chief reason to believe iron is at the core. It is not necessarily all iron, since the field is generated by eddy currents. Molten iron loses its magnetic properties.

There's nothing wrong with the idea that there could be structure in the earth's core. It might come about through some unknown process. All inside of one meter? Surprises seem to crop up in unexpected places, when exploring the unknown.

 

[123jack]

Fairly old thread but I thought I'd mention for anyone else finding it:

It has now been "pretty well" confirmed that there is indeed a molten core that appears to have a solid ball within it.
This was identified by evaluating the frequencies of waves passing through the earth and corelating the time taken for
specific frequencies to travel a known distance.