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So I was in the shower today...
#1
...And I was thinking about various things that teachers tell you that aren't exactly correct.

For instance, I think it was Newton who showed that two cannonballs of different size have the same downward acceleration, disproving an earlier theory that one will fall faster because it is bigger. The earlier theory may have been extrapolated from observing the effect of air on falling objects: lighter (eg. less dense) (and sometimes smaller) objects will fall slower through air.

Some people, and some textbooks, ironically make the same logical mistake: that gravity is the same regardless of the mass of the object in question. This is of course in direct violation of relativity. Objects that are bigger in mass will have higher attraction towards the Earth than smaller objects, but at miniscule ratios this is not visible at all. (In case you would have any doubts about it, think about an object as massive as the Sun attracting the earth. It's gravitational pull towards the earth is much bigger than that of a cannonball)


Now... As I was thinking about this, another thought came up: "the law of universal gravitation" applied to the core of the Earth: the gravitational force between any two objects is their masses multiplied by themselves, multiplied by the gravitational constant, and divided by the square of their distance. (http://en.wikipedia.org/wiki/Law_of_univ...ravitation)

So it is therefore logical that the particle in the gravitational center of the earth has no gravitational forces pulling on it. The particles near it have almost none and so on, until the force starts to decrease due to distance from the center and less change in the cancellation of opposite gravitational forces.

It is then alarming to me that people have assumed that the core of the earth is a superhot heavy solid. Would it not be more logical to predict that it would be a super COLD light GAS instead? That would make all that magma above it actually make a lot more sense...

EDITed.

I'm a genius. :wtnod:
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#2
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#3
1. It was Galileo who did the thing with the cannonballs, not Newton. Big Grin

2. How does a cold gas in the center of the Earth make the magma more logical? O_o

3. Why is it logical that the particle in the gravitational center of the Earth has no gravitational forces pulling on it? Wouldn't it be just as strong as everywhere else, since it's surrounded by lots of other molecules, or even stronger, since pressure is forcing the molecules closer together, thereby greatening the gravitational force? I tried fooling around with the equation, and a 1 mass particle with a distance of 5 exerts less gravitational force than one with a distance of 3.

4. If your theory was true, then we wouldn't exist, because gravity would have stopped working the instant a particle came too close to another one. Unless I've misinterpreted you...
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#4
Actually, the closer you get to the center of a mass, the higher the gravitational attraction is. This increased exponentially (proportional to the inverse of the square of the radius). As a result, the point directly in the center will have infinite gravitational attraction, and ergo, it will be a super hot, dense solid.
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#5
Quote:Actually, the closer you get to the center of a mass, the higher the gravitational attraction is.
True, as you get closer to a mass, but, if you go into that mass, the mass below you would grow less, and so would it's pull of gravity, no? Thus like Agamemnus is thinking, once you hit the center, the remaining mass has lil to no pull, at least towards the center.. There would still be gravity, but pulling slightly outward toward the mass of the Earth surrounding the center....

Course I could be way off, but if you think about it, each atom has it's own gravitational pull in a spherical dirction... It focuses into a larger sphere only as the atoms come together to make larger objects.... So in the center of the Earth, you would get reversed gravity, which would seem like 0 gravity, but it's technicaly still there....

Pull: towards ( <-- away (dead center) away ) <-- towards

Though, I agree with the imposibility of true 0 gravity.. cause like I said before, each atom has it's own gravity, if I remember right.... so where ever a mass is, you will always have some form of gravity....

:roll:
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#6
The point you make is valid until you realise the average of all the atoms of Earth is it's center. And there, the gravitational attraction there is infinite.

If someone was to drill a giant hole directly through the planet that went directly over the center of mass, and you dropped a ball down the hole, it would (with SHM) modulate until it lost all it's energy, and 'hover' directly on the center of mass (obviously assuming it isn't affected by the rest of the universe).
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#7
Quote:so where ever a mass is, you will always have some form of gravity...
Of course, you could always go into the completely crazy field of trying to figure out what gravity actually is, aka: going beyond what is thought to be possible ATM.

And by that I mean, perhaps taking gravity away from a mass. That mass would have no gravitational attraction. Heheh...Sounds hard to do, because I haven't heard of anyone actually telling me what part of the mass is responsible for gravity. Or is it mass itself...hmm... Take away the defining area of mass out of mass, and you have nothing but a form without mass.

Ouch, too confusing.
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#8
Scientists don't properly understand what causes gravitational attraction. Gravity-particles, gravitrons, have been postulated, but there is no proof, it is just a new-age idea. For gravitrons to actually exist, it will require a change in our understanding of Physics, so that might be what is holding the idea back.

What we do understand is the concept of gravitational attraction - again - we understand that it happens, not why it happens.
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#9
Quote:The point you make is valid until you realise the average of all the atoms of Earth is it's (sic)center. And there, the gravitational attraction there is infinite.

If someone was to drill a giant hole directly through the planet that went directly over the center of mass, and you dropped a ball down the hole, it would (with SHM) modulate until it lost all it's energy, and 'hover' directly on the center of mass (obviously assuming it isn't affected by the rest of the universe).

.....

No.

Read the formula. . . .

If a particle was at the center of the Earth, the gravitational forces exerted on it would be 0. You're assuming the Earth is one whole "mass", but that's simply not the case. You don't put the Earth's distance from you into the equation if you're reasonably close to the earth. You must consider all the particles in the Earth or at least a subset of them.

Think about it. If you don't consider each particle in the formula then you can have weird outcomes that violate the law of conservation of mass and energy. For instance, infinite pull at the center. Now how does that make sense?


Rattrapmax6 is correct but I don't quite understand what he means by "slightly pulling outward"...
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EDIT:

thegrogen:

1) OK thanks..

2) Because the highest level of gravity would be located somewhere in between the center and outer core of the earth, where force-of-gravity "cancellations" are smaller. High levels of gravity means high pressure and that means a hot solid or perhaps a hot liquid.

3) Same as explanation to aetherfox. Even if pressure forced them closer together, you would still have little gravity in the center of the earth because of force cancellations.

4) ?????
Peace cannot be obtained without war. Why? If there is already peace, it is unnecessary for war. If there is no peace, there is already war."

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#10
Graviton. Gravitron sounds like some sort of action figure. Big Grin
One of the reasons gravitons, if they exist, haven't been detected is because they are very weak WIMPs (weakly interacting minor particles), even weaker than neutrinos. Some people think that to ever find one we would need a detector the size of Jupiter, and even that would only detect one very rarely.

But do we even need a particle? If ripples in space-time are manifested as gravity, would a particle even make sense?
And another thing, Newton's laws break down at a scale of around 10^-6 metres, and don't work nearly at all around 10^-9 metres. So something needs to be adjusted in any case. (Of course the law of gravitation has discrepancies on massive scales too, that's why astrophysicists came up with dark matter - but maybe it's a problem with the law itself.)

[EDIT] On what aga just said I thought as well - wouldn't the ball at the centre of the Earth move as close as it can get to the sun or moon? Or if you exclude all celestial bodies, then it would move as close as it can get directly underneath the part of Earth with the greatest mass (say, the tallest mountain).
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