Is there confirmed gravity without spin?

lewcos · Apr 6, 2005

Are there any cases where there is an object in space that is not spinning (or spinning very little) that still has a measured gravitational pull in line predictions for a body of its mass? I ask because it seems that spin and mass are the logical causes of gravity and not just the mass as I have read. (or have I just not read enough?)

lewcos · Apr 6, 2005

To follow up...the spinning actually causes a form of suction and we are actually just being sucked to the earth much like on the Roundup ride at a carnival.

larper · Apr 6, 2005

If that is so, then why does something measurably weigh less at the equator than at the poles? The centripetal acceleration at the earth's equator is measurable. Tidally locked moons barely spin. But they have gravity. <div class="Discussion_UserSignature"> Vote Libertarian </div>

kmarinas86 · Apr 6, 2005

All mass has gravitational attraction. Spin is relative to mass. It just creates centripetal forces (specifically, angular momentum). If something was spinning at relativistic speeds, it would experience time dilation and increased relativistic mass. When black holes form, the gravity also pulls matter into it. It starts spinning really fast this way.

kmarinas86 · Apr 6, 2005

Are there any cases where there is an object in space that is not spinning (or spinning very little) that still has a measured gravitational pull in line predictions for a body of its mass? Venus spins very slowly - 243 Earth Days per rotation! http://www.google.com/search?num=100&hl=en&lr=&safe=off&q=radius+of+venus+times+pi radius of Venus times pi = 19 012.2904 kilometers Venus rotates at 3.26 km/hr - that is very slow! That's the speed of a human walking gently... Notice that gravity is not proportional to spin!

vogon13 · Apr 6, 2005

Iapetus is also currently a slow rotator. Roughly 80 days from sunrise to sunrise. Despite controversy about its appearance, spacecraft mass estimates seem normal for a body such as this. If this helps, think about the opposite case. Eons ago earth was spinning faster than it is now. No geological evidence suggests the various minerals and landforms developed under a drastically altered gravitational pull. From this, you can extrapolate in the other direction with confidence. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

Saiph · Apr 6, 2005

Yes there are cases. 1) In the lab, when they empircally determined G by setting big masses next to eachother. 2) Venus: Barely spins, plenty of gravity, directly in line with predictions. 3) If it's a "logical conclusion" why don't you explain the logic? I need an, "If A and B, then C" arguement here. 4) In a rotating reference frame, rotation actually creates a force that pushes you away from the spin axis (the center of the earth in this case), not pulling you towards it. It's called centrifugal force (and while it's an illusion, it's perfectly valid in a rotating reference frame) <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

lewcos · Apr 7, 2005

Thanks for your answers - spinning apparently has no effect on gravity - I hadn't thought through the Roundup ride example too closely - Saiph is right - you are actually being "pushed" not "pulled".

gfpaladin · Apr 7, 2005

4) In a rotating reference frame, rotation actually creates a force that pushes you away from the spin axis (the center of the earth in this case), not pulling you towards it. It's called centrifugal force (and while it's an illusion, it's perfectly valid in a rotating reference frame) When you say 'illusion', I assume you mean the fact that 'centrifugal' force is a fictitious force. It is centripetal force that cause an object to move along a circular path...

CalliArcale · Apr 7, 2005

Centrifugal force isn't exactly fictitious. I think it's better described as a net acceleration. It is quite real, and measurable, even though it only exists in a certain frame of reference. Basically, if you are travelling forwards at a constant velocity and then deflected onto a circular path by a tether, you will perceive an acceleration towards the outside of that circular path. If you are in an enclosed cab and you drop an object, it will seem to "fall" perpendicular to your direction of travel. If, however, you are not in an enclosed cab when you drop the object, the illusion will be revealed when the object travels away at a tangent to the circle -- directly in line with your momentum at the moment you released the object. The farther an object falls in proportion to the size of the centrifuge, and the more obvious the effect will be. One consequence of this is that if you want to create "artificial gravity" with a giant centrifuge, it has to be very big indeed to avoid really screwing you up. Plus, gravity is higher the farther you are from the center, so you don't want it so small that the height of your own body is significant. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

gfpaladin · Apr 7, 2005

Centrifugal force isn't exactly fictitious. I think it's better described as a net acceleration. It is quite real, and measurable, even though it only exists in a certain frame of reference. Actually, it is often refered to as fictitious or 'pseudo'. Here is one example: "Centripetal force must not be confused with centrifugal force. In an inertial reference frame (not rotating or accelerating), the centripetal force accelerates a particle in such a way that it moves along a circular path. In a corotating reference frame, a particle in circular motion has zero velocity. In this case, the centripetal force appears to be exactly cancelled by a pseudo-force, the centrifugal force. Centripetal forces are true forces, appearing in inertial reference frames; centrifugal forces appear only in rotating frames."--online dictionary Another: "It is important to note that the centrifugal force does not actually exist. Nevertheless, it appears quite real to the object being rotated." University of Virginia, Physics Show website Another: "centrifugal force is an enigma. It's not one of the fundamental forces, such as gravity and the electric force. Mathematically, it shows up in frames that rotate along with the merry-go-round or the car that goes around a curve. But, when the same situation is examined from a stationary frame, such as the ground, it does not exist."--a NASA website Specifically "Because the centrifugal force exists only in rotating reference frames, but not in inertial reference frames, it's sometimes called a "fictitious" or "pseudo" force."--http://observe.arc.nasa.gov/nasa/space/centrifugal/centrifugal5.html You ARE correct, however, about it existing in certain reference frames...

CalliArcale · Apr 7, 2005

I know it's often described as a fictitious force, but I think "net acceleration" is more accurate. "Fictitious" tends to imply "somebody made it up", which is not true. People really do perceive it. They're just wrong in thinking that it's an actual force. I have a degree in English. I like to dig around in the meanings and connotations of words. <img src="/images/icons/wink.gif" /> Either way, I think the meaning does get across, so use whichever term you feel best. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

atraxani · Aug 4, 2005

You said, "Basically, if you are travelling forwards at a constant velocity and then deflected onto a circular path by a tether, you will perceive an acceleration towards the outside of that circular path." Actually, you won't. You will accelerate radially inward, not radially outward. Orbiting bodies accelerate inward. Their velocity vector is always tangentential to the circle, and the acceleration vector is perpendicular to their velocity: straight towards the center of the circle. Since the acceleration is perpendicular to the velocity, the velocity changes in direction only, not in magnitude. The direction of the net acceleration is the same direction as the net force, always. The force is exerted inwards, toward the center. It is either caused by gravity, tension in a string, or something else.

atraxani · Aug 4, 2005

Also, you said "People really do perceive it [the centrifugal force]." To illustrate why this is incorrect, consider sitting in a seat in a car. If you press the acceleration pedel, you accelerate forward. The direction of the force is forward. And yet, you will be pressed firmly against the seat behind you. Are you percieving a force that is pushing you backwards? Certainly not. When turning a corner, you will be pushed against the outside wall. Are you percieving a force that is pushing you against this wall? Not in the least.

Saiph · Aug 4, 2005

Actually, inside the reference frame of the car, a object held before you will shift to the outside of the turn, away from the center. Within the reference frame it is accelerated "out". If you switch reference frames however, that isn't so. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

atraxani · Oct 29, 2005

You can't use a non inertial frame under Newtonian mechanics as inertia and Newton's laws do not hold in non inertial frames (accelerated frames). It is neither useful nor meaningful nor accurate to claim that the object in the car is accelerated.

Saiph · Oct 29, 2005

I'm afraid my physics texts would disagree with you. Newtons laws DO hold in accelerated reference frames, they just tend to improperly attribute the acceleration to a phantom force. Take an object in an accelerating elevator. It attributes the motion not to the floor moving up faster, but to a force pushing/pulling the object down. But, this is the risk you run with reference frames in any system. Anyway, you can properly describe the motion of an object using coordinates that are associated with the rotating frame. Such things as the coriolis force result, which is produced, mathematically, by the cross product of the reference frames rotation vector and the velocity vector of the object. http://hyperphysics.phy-astr.gsu.edu/hbase/corf.html I will agree, it isn't a "real" force. However, the motion can be described by applying forces described in this fashion to the object. Thus hyperphysics labeling them as "effective forces". <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Oct 29, 2005

atraxani - Newton's laws of motion are quite accurate and useful in calculations as long as the factors added by Einstein's discoveries are tiny, notably relativity. The rest of this is really semantics. Like, would you consider a scientific textbook listing sunrise and sunset times in various locations and dates to be a superstitious text fostering a geocentric universe? Or would you simply accept the terms as common English idiom adopted by the populace, including scientists? Back to thread theme: I know that ordinary spin is not related to gravity, as noted in the fine answers posted. However, quark spin is quite different in nature. Is there any relationship between quark spin and gravity, or the propagation of both? Do we know how either is propagated - i.e. the actual mechanism?

atraxani · Nov 4, 2005

"Take an object in an accelerating elevator. It attributes the motion not to the floor moving up faster, but to a force pushing/pulling the object down. " What motion? Are you referring to an object on the floor of the elevator? No motion exists if you attach your frame of reference to the accelerating elevator. Newton's laws do not make the correct predictions in accelerated frames. Newton's law of gravitation predicts a force between two masses. Newton's first law predicts that a force will cause an acceleration. In a frame attached to a free falling object, no acceleration will occur, despite the fact that his laws predict that it will. You say that "they just tend to improperly attribute the acceleration to a phantom force." Which Newtonian law states this? Did Newton ever talk about phantom forces?

drwayne · Nov 4, 2005

"Newton's laws do not make the correct predictions in accelerated frames." Actually they do. You just have to account for all the forces in the system, including external forces. Properly understanding, and accounting for the forces acting in a system (inertial or not) is the discipline of solving statics and dynamics problems. Wayne <div class="Discussion_UserSignature"> "1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher </div>

jatslo · Nov 4, 2005

"...Newton's laws do not make the correct predictions in accelerated frames.." <--- (F = ma) is fragmented; Newton, expects us to add, or make more complete (F = ma), because density and viscosity are real, as in reality/relativity.

Saiph · Nov 5, 2005

but they do make those predictions. IL'm using classical mechanics to predict the motion of objects in a rotating (read accelerating) frame right now. Heck, here's a simple accelerating frame that's used all the time: Falling objects. Now, if I attach my reference frame to the elevator, I'll still see the dropped object fall, afterall, doing that is the same as saying I'm in the elevator. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

atraxani · Nov 10, 2005

"Now, if I attach my reference frame to the elevator, I'll still see the dropped object fall, afterall, doing that is the same as saying I'm in the elevator." Yes, but if you attach your reference frame to an elevator, you will see the object fall with a different acceleration. In fact, depending on the acceleration of the elevator, it might appear that the object is falling and accelerating up. Newton's laws predict acceleration as a function of force, and force as a function of gravity. In a non inertial frame, you will observe accelerations different than those predicted by Newton’s laws For example, if you are in an elevator accelerating up at 20m/s^2, and a brick passes by your window, it will appear to you to be moving at 29.8m/s^2. If the brick has a mass of 10 kg, Newton’s law of gravitation predicts a force of 98 newtons between the earth and the brick, which results in an acceleration of 9.8 newtons. That differs from observation, which is why Newton’s laws don't make the correct predictions in non inertial frames. Newton never discussed fictitious or phantom forces or non inertial reference frames, to my knowledge. To make the correct predictions in non inertial frames, Newton's laws must be modified.

nexium · Dec 22, 2005

As far as I know spin does not increase gravity, but defacto decreases gravity except at the North and South Pole. Since all things are relative everything is spinning at least very slowly with respect to something, so we cannot test this theory perfectly. Neil

newtonian · Dec 22, 2005

Neil - I'm not sure everything is spinning - as per my thread questioning whether our universe is spinning slightly. Spin does not actually decrease gravity - it decreases the effect of gravity due to other forces which cause the motion (angular momentum) tending to cancel gravity's effects. Ultimately, spin can cause escape velocity to be reached such that the matter is not gravitationally bound. My earlier question remains: is quark spin related to the generation of gravity? Or, more generally: how is gravity propagated by matter such that the increase in mass of quarks increases gravity? Is this an intrinsic property of quarks, or does it involve something smaller going on within quarks???

Is there confirmed gravity without spin?

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