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syhprum1
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I think a lot of the misunderstanding about "gyros" is due to the friction in the bearings of simple improvised ones a proper gyro with quasi zero friction bearings does not precess
Do you have a reference for that? You seem to be saying that, in the absence of friction in the bearings, the spinning gyro will just fall over from the gravitational torque.syhprum1 said:I think a lot of the misunderstanding about "gyros" is due to the friction in the bearings of simple improvised ones a proper gyro with quasi zero friction bearings does not precess
... that intuition being:curiouscris said:I noted in that second video that when he tried to force the gyro against its direction of precession (not sure what its really called) he couldn't do it. which confirms my intuition about it.
... then yes, that is correct.Now clearly he is lifting it in the direction it is precessing. My guess is he could not force it to go in the other direction and if he attempted that it would drive itself into the ground.
Simon Bridge said:Do you have a reference for that? You seem to be saying that, in the absence of friction in the bearings, the spinning gyro will just fall over from the gravitational torque.
... that intuition being:... then yes, that is correct.
Your other questions in the same post are answered in the videos.
Precession is caused by a torque perpendicular to the axis. Frictional torque in the bearings, which is parallel to the axis, is not required for precession.syhprum1 said:proper gyro with quasi zero friction bearings does not precess
What is "the mass of gravity"?hmmmok said:because as the mass of gravity approaches zero
Why should any mass increase here? The mass of the gyro is constant.hmmmok said:the mass in the centrifugal force equation increases to its max.
That does not really answer the question and sounds cryptic.What was required was an unamabigiouse reply to the question of where exactly is the centre of mass of a spinninig gyro on a stand or string.The implication is that the CoM it is at the centre of the spinning mass but that mass is precessing about a point,"the stand".The mass moves around a point and the answer seems that the point becomes the centre of pressure rather than the CoM.A.T. said:Yes, a definition is always correct, per definition.
OK. Then this will be amply documented - please provide a reference to the documentation. Thanks.Visualise the usual toy gyroscope end on with the wheel spinning clockwise looking at the bearing the friction between the rotating shaft and the bottom of the bearing will tend to push the shaft to right hence the precession.
In professional gyros as are used for navigation either air or magnetic bearings are used to reduce this friction as much as possible as precession is definitely not wanted
No, that is not the answer. It is trivial to design a stand where the CoM precesses around a different point, than the center of pressure (support point).Buckleymanor said:The implication is that the CoM it is at the centre of the spinning mass but that mass is precessing about a point,"the stand".The mass moves around a point and the answer seems that the point becomes the centre of pressure rather than the CoM.
syhprum1 said:The usefulness of a spinning disk in a navigation device is that it tends to stay aligned to the ether/remote galaxies/CMBR or what ever the latest theory is I confess I did not appreciate the purpose gimbals severed that allow the body of the device to move without disturbing the alignment of the spinning wheel.
That's a tautology. It's true for every rigid body in any situation.curiouschris said:it simply stays aligned to itself
syhprum1 said:The usefulness of a spinning disk in a navigation device is that it tends to stay aligned to the ether/remote galaxies/CMBR or what ever the latest theory is I confess I did not appreciate the purpose gimbals severed that allow the body of the device to move without disturbing the alignment of the spinning wheel.
Buckleymanor said:That does not really answer the question and sounds cryptic.What was required was an unamabigiouse reply to the question of where exactly is the centre of mass of a spinninig gyro on a stand or string.The implication is that the CoM it is at the centre of the spinning mass but that mass is precessing about a point,"the stand".The mass moves around a point and the answer seems that the point becomes the centre of pressure rather than the CoM.
Definitions define experiments dictate.
... that is a good quality in a scientist.This was my own idea I confess I was in error !
Please read the links I provided you in my replies ... you have been laboring under a common misunderstanding about how gyroscopic navigation works. Although - certainly - the phenomenon of interest is that a gyro tries to maintain whatever orientation it was in when it was spin up: the gyro does not care about CMBR or what distant galaxies are doing.The usefulness of a spinning disk in a navigation device is that it tends to stay aligned to the ether/remote galaxies/CMBR or what ever the latest theory is I confess I did not appreciate the purpose gimbals [served] that allow the body of the device to move without disturbing the alignment of the spinning wheel.
I agree except that the defined position might not be where it expected to be.There don't seem to be a consensus that the CoM is changeing in it's position as the giro revolves about the stand.This is not a fixed position!You can define the Centre of Mass of a revolving can full off marbles before it rotates but once it moves you cannot.jbriggs444 said:The Center of Mass is a defined position. It is where it is defined to be. Experiment cannot change this. An experiment that measures something else... measures something else.
Buckleymanor said:I agree except that the defined position might not be where it expected to be.There don't seem to be a consensus that the CoM is changeing in it's position as the giro revolves about the stand.This is not a fixed position!You can define the Centre of Mass of a revolving can full off marbles before it rotates but once it moves you cannot.
The CoM is static relative to the gyro. It doesn't move closer to the support.Buckleymanor said:.There don't seem to be a consensus that the CoM is changeing in it's position as the giro revolves about the stand.
Utter nonsense.Buckleymanor said:You can define the Centre of Mass of a revolving can full off marbles before it rotates but once it moves you cannot.
jhmar said:as every baryon (i.e. proton) has a shell of two gravitons
jhmar said:it is the position of the weak gravitons that is altered by spin, creating a local gravity field around the mass of the gyroscope.
Maybe a revolving can full of marbles is not the best example of a spinning object in which the centre of mass is not well defined.So here is one that is http://video.mit.edu/watch/double-pendulum-6392/ If it were possible to define the centre of mass before the Chaotic Pendulum was spun, then it should be also possible to determine the centre of mass, the exact position and speed of the pendulem at any given time when it is spinning.As this is clearly not the case then the centre of mass must change position as the object rotates.jbriggs444 said:Expectations are irrelevant. The center of mass is where it is defined to be. That position is determined by the definition, although it may vary over time. It will not, in general, be directly above the support point. The center of mass of a revolving can full of marbles is perfectly well defined.
And neither is your chaotic pendulum, as there is nothing chaotic about a mounted gyro. And as jbriggs noted, you are confusing defining and predicting. And on top of that, your example is contradicting your own claim, that the CoM moves over the support point when the gyro precesses, because that would be very predictable and not chaotic all.Buckleymanor said:Maybe a revolving can full of marbles is not the best example of a spinning object
I don't recognise that we are speaking past each other it's just that there is a probably a misunderstanding between the mathematical definition you propose and the experimental evidence that I try to explain.Mathematicaly it's obviouse that the CoM should be where it's calculated to be within a chaotic system but expermentaly it is obviouse it's not.Otherwise you would have a pendulum moveing in completely predicatable way.jbriggs444 said:Perhaps we are speaking past each other. The word "define" does not mean the same thing as "calculate", "measure", "predict" or even "determine". I use it in the sense of a mathematical definition. To define the center of mass is to explain what the words "center of mass" mean.
The center of mass of a Chaotic Pendulum is perfectly well defined at all times. By that I mean that we know the meaning of the words "center of mass of a Chaotic Pendulum" at all times and further, that there is no ambiguity -- there is, in principle, exactly one position that is the "center of mass".
What is missing in the case of a Chaotic Pendulum is method for making a precise prediction of that center of mass, given a set of measurements, no matter how precise, of the initial conditions. It is, of course, possible to determine both the position and speed of the center of mass of the pendulum at any given time while it is spinning. It's just not possible to predict this position very far in advance.
Especially since Buckleymanor proposes that the gyro's CoM changes in a very predictable way, as soon as the precession starts. Nothing chaotic about that.jbriggs444 said:The fact that the CoM of a chaotic system cannot be predicted reliably far into the future is completely irrelevant.
Well I can't really argue past that as you recently posted this,." I use it in the sense of a mathematical definition"You have to make your mind up.jbriggs444 said:This is not a disagreement about physics. This is a disagreement about linguistics -- about the meaning of words. I did not propose a mathematical definition. I tried to explain what a "definition" (mathematical or otherwise) is.
The CoM of any system is always where it is defined to be. That is true by definition. No possible experiment can demonstrate otherwise. The fact that the CoM of a chaotic system cannot be predicted reliably far into the future is completely irrelevant. You persist in confusing "define" with "predict".
Seems to me like almost everyone is pretty clear here, including the thread starter, who already acknowledged that his question was answered on the first page.Buckleymanor said:You have to make your mind up.