Do spinning objects really lose weight?

[Dale]

2.You start to whirl the mass in a horizontal circle playing out the string so that it lengthens and you adjust the speed so that the mass does not collide with the earth.

I already told you that this is not relevant. The motion you describe here is not spinning since it is rotation about an axis that does not pass through the object's center of mass.

Let A and B be two arbitrary but identical rigid objects of mass m. A is not spinning, but B is spinning (rotating about an axis through its center of mass). A is experiencing a net external force f and therefore A's center of mass is accelerating at a rate a=f/m. The center of mass of B is also accelerating at the same rate a. From Newton's 2nd law the force acting on B is also f. Therefore, since the forces must be equal a spinning object must weigh the same as a non-spinning one.

 

[Dadface]

DaleSpam you seem to have dismissed a system I chose to analyse on the basis of the word "spinning".I have already referred to this word and its definition in post 32,please take a look.May I also point out that the analysis,in principle,also applies to an extended system on a spindle.
As for your second point I am assuming you mean that the "arbitary objects" are identical
in terms of the predictions made by Newtons laws.They are not by virtue of the fact that one is spinning and the other is not spinning.If the spinning object was balanced on a very thin spindle it can remain spinning until It slows down enough so that it falls over.In principle you may be able to balance the non spinning object but it will be in a state of unstable equilibrium,the slightest wobble and over it goes.Newtons laws,therefore, make different predictions for the two objects,predicting that whilst the spinning object is going at a fast enough rate it will not fall over even when there is a slight wobble.These predictions,of course, are confirmed by observations.
There are several other differences and even the elastic properties of the spinning object are relevant to the analysis when this is carried out in even greater detail.Early in this thread jambaugh introduced S.R into the analysis and pointed out that the spinning object becomes more massive.The mass changes may be extremely and immeasurably small but nevertheless we can feel fairly confident that there are changes.
If we get back to classical physics Newtons laws require that each point object,be it a single particle or one just one component part of a macroscopic object,requires a centripetal force for it to remain in its curved path.The main difference between my analysis and those that are conventionally carried out is that I show that the weight of the object itself contributes to the centripetal force needed,even when the plane of rotation is horizontal.
Can we agree that a full detailed analysis of rotating/spinning objects is very complicated?

 

[Doc Al]

As for your second point I am assuming you mean that the "arbitary objects" are identical
in terms of the predictions made by Newtons laws.They are not by virtue of the fact that one is spinning and the other is not spinning.If the spinning object was balanced on a very thin spindle it can remain spinning until It slows down enough so that it falls over.In principle you may be able to balance the non spinning object but it will be in a state of unstable equilibrium,the slightest wobble and over it goes.Newtons laws,therefore, make different predictions for the two objects,predicting that whilst the spinning object is going at a fast enough rate it will not fall over even when there is a slight wobble.These predictions,of course, are confirmed by observations.

But the prediction that you are making, that the "weight" is different for a spinning object, is not confirmed by experiment.

There are several other differences and even the elastic properties of the spinning object are relevant to the analysis when this is carried out in even greater detail.Early in this thread jambaugh introduced S.R into the analysis and pointed out that the spinning object becomes more massive.The mass changes may be extremely and immeasurably small but nevertheless we can feel fairly confident that there are changes.

None of which has anything to do with what you are claiming about spinning objects.

If we get back to classical physics Newtons laws require that each point object,be it a single particle or one just one component part of a macroscopic object,requires a centripetal force for it to remain in its curved path.The main difference between my analysis and those that are conventionally carried out is that I show that the weight of the object itself contributes to the centripetal force needed,even when the plane of rotation is horizontal.

Again you equivocate between "an object being twirled on a string" and "a spinning object". Sure, if you twirl an object on a giant string, then the direction of the gravitational force will have a radial component. That's a far cry from making a claim about the apparent weight of a spinning object.

 

[Dadface]

Doc Al spinning, turning,rotating, orbiting choose whatever word you prefer, the principle is the same.Sketch a giant disc ideally with most of its mass concentrated on its outer edge,being supported above a round earth,mark in the gravitational forces, particularly at the outer edges,and see the radial component.Now set the disc spinning and watch the disc support system changing ,stretching etc so as to accommodate the resulting centripetal force.Now ask yourself the question- "Is it changes in the support system only that provides the centripetal force"?.The answer is no ,the weight provides some of the centripetal force the amount of which depends on the geometry and structure of the system, the speed of rotation and the radius of the circle.

 

[Dale]

DaleSpam you seem to have dismissed a system I chose to analyse on the basis of the word "spinning".I have already referred to this word and its definition in post 32,please take a look.

Yes, I am dismissing the system you chose to analyse. It is irrelevant to your own OP. In your OP you specifically referred to gyroscopes. Gyroscopes spin, so an analysis of orbital motion is simply not relevant as both turin and I have pointed out.

Your use of a dictionary definition of the word "spin" is also not relevant. Word useage in physics is much more precise (and mathematical) than in general useage. In physics, spinning is rotation about an axis that passes through the object's center of mass. Gyroscopes spin. Satellites orbit. Analysis of orbital motion is not relevant to the OP about gyroscopes.

Everybody here knows that orbiting objects have less apparent weight than non-orbiting objects and nobody is disputing that. Everybody (besides you) also knows that the fact that orbiting objects have less apparent weight is irrelevant to the question about whether or not spinning objects have less apparent weight.

May I also point out that the analysis,in principle,also applies to an extended system on a spindle?

I don't think so. If you think it does then please demonstrate that.

 

[Dadface]

In my OP I referred to "gyroscopes and the like" and when I presented an analysis I did so by referring to a point object and I have stated that the effect on a whole object can be found by integration,so it does apply to gyroscopes as well as to orbiting objects.
With your second point I have been dismissed on a point of semantics.
With your third point I am told that everybody here besides me knows that the apparent weight loss of orbiting objects is irrelevant to the question about spinning objects this being despite the fact that I have been pointing out that with a spinning object there is a horizontal weight component and that the spinning object can be described as being in partial orbit.
With your fourth point you seemed to suggest that my analysis cannot,in fact,be applied
to an extended system. If you think this is true then please demonstrate that.May I suggest that you read my previous post.

 

[Dale]

I have stated that the effect on a whole object can be found by integration,so it does apply to gyroscopes as well as to orbiting objects.

Then please perform the integration and demonstrate that your analysis also applies to spinning objects rather than just orbiting objects.

you seemed to suggest that my analysis cannot,in fact,be applied to an extended system. If you think this is true then please demonstrate that.

I asked you first , besides the burden of proof is always on the person making the unorthodox claim.

 

[Dadface]

Thank you Dalespam, Doc Al and everybody else, especially turin. I found all of your feedback useful and it forced me to think through things more carefully.I think I have already done the maths correctly but I am going to get this checked out.If I knew how to post a smilie face I would do so here.

 

[turin]

turin thank you very much indeed for presenting your maths.

You are quite welcome.

I refer to the "horizontal massless rod of length 2r".The rod cannot be horizontal otherwise there is no component to support the weight .

This is simply untrue in my model. I clarify that the horizontal rod in my model is perfectly rigid, and it isn't even supposed to represent a real rod, but an infinitesimal slice of a disk that supports the massive ring of the gyroscope. There is nothing wrong with the rod remaining horizontal and supporting the weight of the gyroscope. I suppose I should have also calculated the balance of torques, but I was too lazy. In short, the symmetry of my model leads to a balance of torques.

You can always point to something in a model that fails to perfectly represent nature. So, of course, if you insist on finding something in the model that does not perfectly describe nature, then no one on this forum, or anywhere else in the physics community of whom I am aware, can offer you a satisfactory contention. Why not object to the infinitesimal thickness of the ring, or the use of massless rods (or strings)? And what of the Ehrenfest Paradox?

If you want to start introducing the effect of material properties (as it seems that you do from one of your comments to DaleSpam), then count me out.

 

[Dadface]

Hello turin.In principle your model differs from mine in one respect.I see that the horizontal rod bends, although very slightly for a "rigid" rod and when I take into account all of the angles involved,including those for the weight vectors, I obtain a different answer.Basically I am just being fussy ,overly so perhaps for a normal gyroscope where we can assume that any bending etc is negligibly small in that any changes become difficult,if not impossible to measure.Thank you again,I really appreciate your feedback and perhaps we will meet in other threads.