Gravity is a vector, it has direction. Each part of the Earth exerts gravitational attraction on every other part. You can compute the force any particular point within the Earth feels due to all the other parts of the Earth using some vector calculus. I have shown you the link to the mathworld page on this before, but it went right over your head.

The situation can also be simplifed by using other results. Newton's shell theorem for one and in the case of the centre of the Earth, simple geometric considerations.

Both of those point towards a perfectly symmetry system at the centre of the Earth. The material which makes up the Earth is pulling you equally in all directions, you feel no net acceleration when at the centre of the Earth.

HOWEVER (since you always seem ti fail to understand this part), that doesn't mean that things are not attracted to the centre of the Earth. Everywhere else, the material there is being attracted to the centre of the Earth, the attraction just gets weaker the closer you get to the centre. Therefore if you put a mixture of heavy and light elements inside the Earth when it's liquid (so they can move about), the heavier elements will sink down to the centre, making the lighter elements float up, because they still feel a gravitational attraction towards the centre of the Earth.

You don't seem to be able to seperate potential, force and pressure in your thinking. You complain again and again and again about the same things but you're utterly unwilling to actually think about them or to learn the maths required to derive results like Newton's shell theorem. Hence you end up saying "But it's wrong" while being completely ignorant of any of the mechanics.

If one drilled a hole through the earth and threw a rock into the hole, assuming no friction, the rock would act like it was on a spring, with maximium velocity at the center, i.e., zero gravity. If we add friction, (rock and feather), the rock will fall further to the center.

One thing that is ignorred is that heavy atoms are not the densest thing at extreme temperature and pressure. In a star, a metal like iron will retain a lot of inner electrons, whereas something like C or O will be fully ionized. Iron's density is its mass/divided by its volume which includes all the space occupied by those tightly held electrons. Fully ionized C is actually denser since its mass occupies much less space (m/v).

That is why neutron stars end up with neutron density instead of finalizing as the highest elements. These are too fluffy at extreme pressure, while smaller stuff is much denser and can pack tighter.

Let us look at pure iron subjected to extra pressure and temperature. If we keep on squishing the iron, the electron clouds will repel and outer electrons will ionize. For the volume to get smaller still, the very stable inner electrons need to ionize. As these ionize, the nucleus charge repulsion will increase at the same time pressure is trying to reduce the volume. The combined affect will cause fission into smaller atoms with their smaller inner electron cloud volumes. Most stellar models have iron and heavies in the core. But in reality these should be floating out of the core.

Although iron will float out of the core, as iron leaves the core, temperature will cool changing the parameters for higher density. As soon as C, O, N, etc, gain any electrons a density inversion will occur, more in line with current expectations.

If we start with a core of small fully ionized atoms at extreme pressure, and lower the pressure a vacuum of sorts will occur, since these little ionized atoms occupy less space than what is possible at that lower pressure. The "vacuum", creates an endothermic situation that is satisfied by fusion so inner electrons an occupy the extra space. It is sort of like a condensation of fog into water dropplets that give off heat of fusion. But in this case, the inner electrons captured equalize the density. The solar flare shows that this type of fusion is not a very effecient, with most of the expansion propagating all the way to the surface.

If you are standing on the surface of the Earth, you will experience 1 g.

If you dig down 10 miles underground, you won't weigh as much because you have 10 miles of dirt that WAS pulling down on you before, but now its pulling you UP on you, (away from the center).

Note, 10 miles is nothing. The effect will be exacerbated the further down you go.

You have to remember that objects are not attracted to the "center" of the planet. They are attracted in the direction where the most mass is, which is past the center, on the other side of the world, from your point of reference.

Amrit: There is a reason why heavier materials sink and lighter materials rise, even in the limit of low gravity. http://en.wikipedia.org/wiki/Buoyancy

AlphaNumeric: Ever get around to the highly impractical Submarine paradox in GR? (It is apparently an Buoyancy-related inconsistency in SR which requires GR to solve.) It's impractical because SR effects are out of the realm of nautical design.

MDT: I derived hole-through-the-Earth as being a diameter on this board. http://forum.physorg.com/index.php?showtop...ndpost&p=131511

Latrosicarius: You are correct, if you work under the assumption that the Earth is of constant density. Light crustal rocks may fool your expectations, however. http://forum.physorg.com/index.php?showtop...ndpost&p=109998

ho rpenner
i read on home page you mention
it does not convince me

In General Theory of Relativity gravitational force is result of curvature of space. Stellar objects change geometry of space. Bigger is mass of a stellar object, more space is curved, bigger is gravitational force.
With “Loop Quantum Gravity” of Carlo Rovelli idea arises that space has a granular structure. Space is made out of “quanta of space” that have a volume of Planck (1).
Speculation in this easy is that there is a link between granular structure of space and its curvature. If space is made out of grains (quanta of space) it is possible that space has different density D. Density D of space depends on the amount of mass in a given volume of space. Higher is density of mass, lover is density of space and opposite. This view is in accord with second law of thermodynamics according to which every system has a tendency to the homogeneous distribution of energy. Also in the universe there is a tendency that energy is distributed in a homogeneous way. We have two basic energies in the universe: energy of matter and energy of space (gravitational energy) that are distributed in a homogeneous way: where density of matter is high density of space is low and opposite. Density D of space in a center of a stellar object is where m is a mass of a stellar object.
In a centre of stellar object density D of space is low regarding space far away of stellar objects. Low density of space causes that in a given volume of space number of quanta of space is smaller than in a given volume of space far away of stellar objects. This low density of space causes that space is stretched and has tendency to shrink. This “shrinking force” of low density space is gravitational force. More density of space is low, more space is curve, and stronger is gravitational force.
Gravity force acts between quanta of space, it is a “short distance force”. Gravity does not work directly between stellar objects, it works in space in which are existing stellar objects. For example space around sun has tendency to shrink and this is gravitational force that pulls planets towards the sun.
Gravity here presented is acting into space and not in between stellar objects. Regarding gravitational force between stellar objects this view is in a perfect accord with General Theory of Relativity. Regarding gravitational force inside stellar objects this view has a different approach. Gravitational acceleration g depends on the density D in a centre of stellar object and on the distance r from the centre: g = G / (D x r on square)
, where m is a mass of stellar object G is gravitational constant and r is distance from the centre.

g = (m x G) / r on square
g = G / (D x r on square)

According to this view gravitational acceleration g changes by going from the surface to the centre of stellar object differently as predict Newton Shell Theorem. We are proposing measuring of gravitational acceleration in “Golden Mine Shaft” in South Africa on the surface and 4200 under surface at the point T in order to get experimental data.

Gravity Density Space Theory (GDSP) explains why heave elements are in the central area of stellar objects: because gravity is most strong there. One can prove that with a simple experiment: you take a glass tube and put in balls with same diameter and different mass. Most heavy balls are black, heavy are brawns, light are green and ultra light are blue. You shake a tube for a while and you will see that black balls are on the bottom, it means most close to the centre of the earth and blue balls are on the top, it means most far from the centre of the earth.
Same is situation with heavy elements situated in the central area of the earth. As gravity attracts them more than light elements in a process of formation of earth heavy elements have been placed there.
Existent theory of gravity has no satisfying explanation how is possible that heavy elements are placed in the central area of the earth. According to existent gravitational theory gravity force diminishes towards the centre of earth which means that in the central area centre should be placed light elements.


References:

(1) Rovelli C. (1997) Loop Quantum Gravity, Living Reviews in Relativity
http://relativity.livingreviews.org/Articles/lrr-1998-1/

(2) Sorli A., Sorli I. (2005). A-Temporal Gravitation And Hypothetical Gravitational waves Electronic Journal of Theoretical Physics, Vol 2, Num 5

(3) Loinger A. The gravitational waves are fictitious entities - II
http://arxiv.org/vc/astro-ph/papers/9904/9904207v1.pdf

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sorli.bistra@gmail.com