Gravity: Does The Rotation Speed of a Body Effect It?

The fact that Venus rotates at 1/250th the speed of Earth and yet has the same gravity seems counter-intuitive to me. One would think that the rotational speed of a body would have a direct (i.e., proportional) bearing on the gravity it produces

 

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No; there is no direct relationship at all.
The only relationship between gravity and rotation is the one mentioned by Pete; that is the centrifugal force at the equator acts to decrease the pull of gravity very,very slightly.

Gravity is caused by mass and not by rotation.

 

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With all due respect, If that is indeed the case, then a motionless body in space, of similar mass, would exhibit gravity similar to one which rotates.... but to my understanding, that is not the case....rotation must be a key ingredient, with regard to gravity, on some level... is it not?

 

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I am under the impression that the while the gravitational effect is due almost 100% to the mass&density involved, and not movement - the roation is a part of what creates the electromagnetic field. This is due to the internal movement of metals in the core. might you be getting the two fields mixed up?

 

Quite simply, your understanding is wrong.
You might be getting confused because there is a hypothetical method for simulating gravity on board a spacecraft by rotating the ship along its axis; this does not produce gravity, but the centifugal force produced can feel a little like gravity to someone standing inside the ship.

 

So then, what you are saying is that a body, similar in density / mass to Earth, would have the identical gravity as Earth, even if it were not rotating in space on its axis...... how can this be?

 

But that is the case.

 

Please forgive my ignorance - I thought I was in the midst of those who somewhat understood Astronomy, Exobiology, & Cosmology..... Jocariah

 

Perhaps J is considering that a rotating body will have a centrifugal force acting counter to gravity thereby REDUCING effective gravity to some extent? It not a direct influence on how much gravity the body has, but rather a reduction of the net effect of the gravity, and limited to the body itself: rotation of the Earth results in a slightly lessened net effect of gravity so that if you were on the equator and weighed a object, then moved to a pole and again weighed the object, the polar weight would be slightly greater than the equator weight. However, the moon or the space station would have no changed reaction to Earth's gravity if was spinning or not, ACCORDING TO CURRENTLY PROVED gravity theory.

There are theories, including Geometrodynamics ( General Relativity ) which have predicted that uncharged spinning objects develop gravitomagnetism: laboratory tests have failed to detect it. There is an ongoing satelite experiment called Gravity B which is scheduled to publish results in a few months. Needless to say, if Gravity B finds no gravitomagnetism there will be a bit of excitement among Relativitysts and antirelativitysts alike.

If gravitomagnetism becomes a proven part of gravity theory, then the spin of a body will have to be considered to contribute to its total, real gravity.

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I think J's concepts are right

but what is actually rotating is always open to debate

Is the massive body rotating or is the Universe ?

If there were no EM fields, and an absolute space.... therefore absolute stillness, then I suspect "gravity" would not exist and any "attraction" would be purely magnetic.

Fortunately the Universe's BXE fields are spinning, linked cosmic to local, so gravity is induced on all bodies.

The actual rotation about an axis of a massive body is therefore only a minor consideration because the BXE spin around Earth is 7.91 km/sec at the surface, while the surface rotational velocity of Earth is about 0.5 km/sec.

The rotation rate is dwarfed by the BXE spin rate.... which causes gravity.....


(personal communication with God.... LOL.)
I suppose this becomes a believe it or not.... most don't believe this.

 

You're correct in saying most don't believe this.

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In fact you'd be even more correct to say that very, very few would accept it.

While it's true that we don't understand exactly what gravity is, we know very well what produces it. Mass. And the rotation of a body doesn't figure into it.

Gravitation computations are made every time anything is launched into space and every time a probe uses a planetary gravitation field to do a "slingshot" on the way to it's next assigned destination. And rotation effects are only considered in one very specific part of all of it - the boost that a spacecraft gains by being launched eastwards. That saves a little bit of fuel, that's all.

Otherwise, rotations are completely ignored. Period.

 

>> In fact you'd be even more correct to say that very, very few would accept it. >>

indeed, but what would they know, LOL.

>> Otherwise, rotations are completely ignored. Period. >>

well "rotations" are ignored because field spins (orbital parameters) rule, OK.

PS:- field spin is a rotation in the cosmic sense

 

Jocariah,

I would like to confirm that the rotation of a body in the classical realm of physics (i.e. non-relativistic) has zero to do with the gravity it produces. Rotation is not a factor. Mass alone determines the strength of one body's mutual gravitational attraction to another.

 

But it is the case. In fact you started this post with an example of two bodies of similar mass having the same gravity even though their rotation rates were greatly dissimilar. The Solar system is full of cases where the gravitational pull of a body bears no relation to its rate of spin.

The only thing needed for gravity is mass.

 

Why do you think so?
Why do think that rotation is so important for gravity, while other properties (like temperature for example) are not?

 

HELLO! IS THIS MIKE TURNED ON?

If Gravity B proves gravitomagnetism, as predicted by General Relativity, then spin will be a minor factor in a body's gravity. If Gravity B shows gravitomagnetism false, only mass will dictate a body's gravity.

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Yes, but a very, very minor factor.

 

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Unclear post.

What is a very, very minor factor.

 

Gravitomagnetism is responsible for an effect known as "frame dragging". It's an effect so subtle that Gravity probe B is equipped with 4 gyroscopes. The gyroscopes are the most perfect spheres ever made. Frame dragging implies the rotation of spacetime around an spinning body.The gyroscopes should be able to detect frame dragging, but it is possible that is so weak that the data of Gravity Probe B can't prove its existence. The probe is also searching for the manifestation of another effect predicted by GR: the geodetic effect

Gravity probe B finally collected all the data needed recently, and now the results are being analyzed, as informed in this paper

http://www.universetoday.com/am/publish/gravity_probe_b_finished.html

 

Thanks, I'm with you now.

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And I agree. If it's proven it will still be a very tiny amount.