Center of Gravity; oxymoron

[sunspot]

I would like to present something interesting for contemplation. The term center of gravity is a mathematical concept that makes dealing with the gravity between objects easier. But if one looks at the center of gravity of say a sphere, the gravity force vectors will all cancel, such that the center of gravity has no net gravitational force.

[□h=-16πT]

A body under the influence of the field of some other body doesn't feel the effect of the force vector pointing in the opposite direction, so they don't cancel out.

[J.C.MacSwell]

I would like to present something interesting for contemplation. The term center of gravity is a mathematical concept that makes dealing with the gravity between objects easier. But if one looks at the center of gravity of say a sphere, the gravity force vectors will all cancel, such that the center of gravity has no net gravitational force.

 

This is only true for the portion of a constant density sphere that an object is "inside of".

[yammers]

Isn't that called the barycenter?

[[Tycho?]]

I would like to present something interesting for contemplation. The term center of gravity is a mathematical concept that makes dealing with the gravity between objects easier. But if one looks at the center of gravity of say a sphere, the gravity force vectors will all cancel, such that the center of gravity has no net gravitational force.

 

Yeah, that doesn't really have anything to do with the actual meaning of center of gravity though.

[sunspot]

If we look at a sphere of metal with a tiny hollow core, an object in the tiny center will see gravity pulling it radially outward in all directions. Shouldn't this summation effect stemming from gravity place the center object under tension instead of compression?

[Sisyphus]

It has neither tension nor compression inside the hollow. There's no tension because every atom in the object is pulled equally in all directions, hence there's no tendency to pull apart. Of course, there is enormous pressure at the center of the Earth, for example, even though there's no gravitational force there, since there is gravitational force on the rest of the earth, and it's all being pushed together.

 

Of course, none of this has anything to do with what is meant by "center of gravity," so I don't really see what we're supposed to be contemplating.

[timo]

Perhaps it would help if someone of you would post what the "center of gravity" is ...

[Sisyphus]

Perhaps it would help if someone of you would post what the "center of gravity" is ...

 

Eh. It's easier to be snide. Anyway, I think Wikipedia does a pretty good job.

[yammers]

I would like to present something interesting for contemplation. The term center of gravity is a mathematical concept that makes dealing with the gravity between objects easier. But if one looks at the center of gravity of say a sphere, the gravity force vectors will all cancel, such that the center of gravity has no net gravitational force.

 

I don't think "center of gravity" is the right term for this, since it refers to the concentration and distribution of mass; where what you want to discuss, (which I'm sure is related to CG) is the gravity factory? of a mass.

 

I think you're right, but this should only be true in deep space where there was no other gravity, because a mass like the moon (or sun) must have an effect on the exact position of the equal gravity core. With that said, I'm not sure that this core would actually be in the very middle (center); with the moon orbiting, this core may be continuously changing it's position...???

[sunspot]

Here is another paradoxical example which may help make things clearer. There is a position between the earth and the sun where one would become weightless due to gravity pulling equalling in both directions. One would not fall either way. If we remove one of these two large masses, our weight will increase, even though the total mass of the system has decreased. Since weight is Mg and mass has decreased, the effects of gravity have increased.

 

What the implication of this analysis is, gravity waves can cancel, where the crest of one wave can cancel the trough of another. When we removed one of the masses, we also removed one of the wave sources. This implies that gravity waves use wave addition where an opposite gravity force direction reverses the crests and troughs. In the example above, we have two decaying sine waves (with distance) above and below x-axis, decaying in opposite directions, but canceling completely where the wave crest/trough of the two decaying waves are the same height.

 

Let me clarify this further by looking at the center of a star. If we assume spherical symmetry there is always a complement point on the opposite side where the waves will cancel, such that the center will have no gravity due to the waves canceling. But at the same time, this does not mean that there are not a huge number of gravity waves in the field at the center, only that the center is a point where all the waves in the field overlap and cancel.

 

If one assumes a strong gravitational field in the center of a star, with umpteen waves all cancelling out, and one also assumes the conservation of energy, then it follows that all this canceled out gravity energy needs to go somewhere. The most logical place is into increased mass and/or increased mass density.

 

If one looks at mass, it is composed of tiny units. Even in stars the high mass is mostly space. The increased mass or mass density could mean increased mass and/or decreased distance between mass. Within stars, the increased mass and/or decrease distance due to the conversion of gravity into mass density, within its center, is burnt off via fusion. My hope is that this little change of perspective will make it possible for the standard theory to become complete. In other words, for jollies, use these assumptions and see what happens.

[BhavinB]

'Gravity at center' and 'Center of gravity' are different things. Yes the 'gravity at center' of a sphere is 0 in all directions, but the 'center of gravity' (and the center of mass) is at the exact center of the sphere.

[[Tycho?]]

Here is another paradoxical example which may help make things clearer. There is a position between the earth and the sun where one would become weightless due to gravity pulling equalling in both directions. One would not fall either way. If we remove one of these two large masses' date=' our weight will increase, even though the total mass of the system has decreased. Since weight is Mg and mass has decreased, the effects of gravity have increased.

 

What the implication of this analysis is, gravity waves can cancel, where the crest of one wave can cancel the trough of another. When we removed one of the masses, we also removed one of the wave sources. This implies that gravity waves use wave addition where an opposite gravity force direction reverses the crests and troughs. In the example above, we have two decaying sine waves (with distance) above and below x-axis, decaying in opposite directions, but canceling completely where the wave crest/trough of the two decaying waves are the same height.

 

Let me clarify this further by looking at the center of a star. If we assume spherical symmetry there is always a complement point on the opposite side where the waves will cancel, such that the center will have no gravity due to the waves canceling. But at the same time, this does not mean that there are not a huge number of gravity waves in the field at the center, only that the center is a point where all the waves in the field overlap and cancel.

 

If one assumes a strong gravitational field in the center of a star, with umpteen waves all cancelling out, and one also assumes the conservation of energy, then it follows that all this canceled out gravity energy needs to go somewhere. The most logical place is into increased mass and/or increased mass density.

 

If one looks at mass, it is composed of tiny units. Even in stars the high mass is mostly space. The increased mass or mass density could mean increased mass and/or decreased distance between mass. Within stars, the increased mass and/or decrease distance due to the conversion of gravity into mass density, within its center, is burnt off via fusion. My hope is that this little change of perspective will make it possible for the standard theory to become complete. In other words, for jollies, use these assumptions and see what happens.[/quote']

 

Well I stopped reading when I got to the gravity wave part. What in the world is producing gravity waves in your example?

[sunspot]

The wave-particle duality of gravitrons?

[JustStuit]

Since gravity pulls to the center of the mass creating it, I don't think there are any forces if you are in the center without any outside forces.

[[Tycho?]]

The wave-particle duality of gravitrons?

 

..sure. My question was what was producing them in your example.

[DaveC426913]

...There is a position between the earth and the sun where one would become weightless due to gravity pulling equalling in both directions.

Yes.

 

What the implication of this analysis is, gravity waves can cancel, where the crest of one wave can cancel the trough of another.

No. That does NOT follow from your earlier statement.

 

The NET force may be zero, but the GROSS force is still the sum of the two.

 

If you replaced the Sun and Earth with two black holes a short distance to each side of you, you can sure bet you'd feel yourself being pulled apart...

[s pepperchin]

If you replaced the Sun and Earth with two black holes a short distance to each side of you, you can sure bet you'd feel yourself being pulled apart...

 

If you replaced the Earth and the Sun with black holes so that you were still at a langrange point than you would not be pulled apart by them.

[gcol]

Is there not, theoretically, one or more lagrange points, however dynamic, where all the forces of gravity cancel each out? Is it not possible that each gravitational system of whatever compexity, can be resolved to such a point?

[JustStuit]

If you replaced the Sun and Earth with two black holes a short distance to each side of you, you can sure bet you'd feel yourself being pulled apart...

 

If you replaced the Earth and the Sun with black holes so that you were still at a langrange point than you would not be pulled apart by them.

Well the black holes would interact with eachother and probably join together and then pull you apart if you're not sandwiched along the way.

[Norman Albers]

With any 1/r potential such as electric or gravitational fields, the force inside of any spherical shell is zero, period! Now if you came from outside to be there, work was done and energy exchanged. Once you are through the spherical shells, though, work is finished. This is assuming there is no further mass at lesser radius.