Is the absolute center of a spinning object moving or stationary?

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Is the absolute center of a spinning object moving or stationary?

I was hoping to find more info online about this than I did. Does anyone know? Is there a better way to frame the question in order to get better search results?
 
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Tinker Grey

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Is the absolute center of a spinning object moving or stationary?

I was hoping to find more info online about this than I did. Does anyone know? Is there a better way to frame the question in order to get better search results?
I think it may depend on what one means by an "absolute center". If one means a dimensionless point that would be the center of the center of center ad infinitum, then I don't what it means for it to have motion. If one means a part of the object that is "effectively" the center, then I don't know what it means for it to be "part of the spinning object" and not spin.
 
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Occams Barber

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Is the absolute center of a spinning object moving or stationary?

I was hoping to find more info online about this than I did. Does anyone know? Is there a better way to frame the question in order to get better search results?


Interesting.

Given the huge spaces between sub-atomic particles I suspect that, statistically speaking there is nothing at the absolute centre of a spinning object apart from an electromagnetic(?) forcefield.

But I could be totally wrong. :(

OB
 
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Petros2015

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Is the absolute center of a spinning object moving or stationary?

The absolutely center of a spinning object
Would be the absolute center of 1 atom
At the absolute center of the object.
Go look at what's in the absolute center of 1 atom
And I think you'll have your answer


Strange, but similar. I'm guessing the force of earth's gravity is 0 at the earth's center; there would be as much mass pulling away from it in all directions as there was pulling towards it. If we made you a little 10' bubble room at the core out of Unobtanium and positioned it right, you'd be in 0g, I think
 
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sjastro

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The very centre of a rotating disk is stationary relative to an object which is not at the centre.
This has been exploited to test gravitational time dilation where an object at the centre is in an inertial frame and an object on the perimeter is in an accelerated or rotating frame.

sjastro said:
A 1960s experiment using radioactive Fe⁵⁷ and Co⁵⁷ nuclei provides the answer.
Fe⁵⁷ nuclei have the interesting property (Mossbauer effect) of emitting and absorbing photons without the nuclei recoiling resulting in the photons being within a narrow frequency interval.

The experiment involves placing Co⁵⁷ nuclei as an emitter at the centre of a rotor that can be operated at 30,000 RPMs to give accelerations 65,000X greater than gravity and Fe⁵⁷ nuclei on the perimeter of the rotor as the absorber.
Since both Co⁵⁷ and Fe⁵⁷ emit and absorb photons at the same frequency respectively when in a stationary or inertial frame they are essentially synchronized clocks.
The experiment can be analysed as the inertial frame of the emitter using special relativity or as the accelerated frame of the absorber using general relativity.
When the rotor is not operating the photons emitted from the centre are absorbed at the perimeter.
At 30,000 RPM absorption is largely reduced as Co⁵⁷ and Fe⁵⁷ nuclei are no longer emitting and absorbing photons at the same frequency.

In the inertial frame the photon’s frequency change is due to the transverse Doppler effect or gravitational time dilation in the accelerated frame.
In the accelerated frame the Fe⁵⁷ nuclei can only absorb the photons at a lower frequency which corresponds to the moving twin's clock running slower.
Is the James-Webb telescope a threat to Christians?
 
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jacks

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Relative to this question, I've often wondered if the outer edge of a rotating disk (like a record) is spinning faster than areas close to the middle. It seems it must travel a greater distance in the same amount of time.
 
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sjastro

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Relative to this question, I've often wondered if the outer edge of a rotating disk (like a record) is spinning faster than areas close to the middle. It seems it must travel a greater distance in the same amount of time.
The tangential velocity Vr does increase with increasing radius r for any given RPM ω.
Tangential-Velocity.jpg
 
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jacks

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The tangential velocity Vr does increase with increasing radius r for any given RPM ω.
Tangential-Velocity.jpg
Thank you for this information. I wonder if you had a disc big enough if the outer edge could travel faster than light.
 
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sjastro

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Thank you for this information. I wonder if you had a disc big enough if the outer edge could travel faster than light.
I'm afraid not the equation is based on low velocity Newtonian physics; special relativity is the relevant theory at very high velocities, the effects of which are described in post #5 as a transverse Doppler effect.
 
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jacks

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I'm afraid not the equation is based on low velocity Newtonian physics; special relativity is the relevant theory at very high velocities, the effects of which are described in post #5 as a transverse Doppler effect.
I knew this would quickly get above my head...So at some point the tangential velocity formula breaks down? I'm afraid to ask, but is there a simple explanation as to why? If it is too much trouble to explain it to a physics dropout, no problem. I've derailed the thread enough already. :)
 
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sjastro

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I knew this would quickly get above my head...So at some point the tangential velocity formula breaks down? I'm afraid to ask, but is there a simple explanation as to why? If it is too much trouble to explain it to a physics dropout, no problem. I've derailed the thread enough already. :)
To accelerate an object with mass up to the speed of light c requires an infinite amount of energy.

energy.jpg

The green curve which is the classical or Newtonian physics does not make this prediction.
The red curve based on special relativity shows the speed of light is the limit, no amount of energy will accelerate an object to the speed of light let alone beyond it.
Massively powerful particle accelerators such as the LHC can accelerated protons up to 0.9999X the speed of light.
 
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Petros2015

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To accelerate an object with mass up to the speed of light c requires an infinite amount of energy.

Because the mass increases

You lose the buoyance of the universe
when you try to move that fast and you'll start hydroplaning out of it
Just like if you were in a swimming pool with a friend
and tried to lift your friend out of the water

It's easy at first
But the more you get him out of the water
The heavier and heavier he gets
So the more and more energy is required
When you try to take something with mass
To the speed of light
It appears to get more and more massive
requiring more and more energy
To get up to light speed

An infinite amount to get it to 100%
Because it's effectively become
Infinitely massive
Leaving the buoyancy of Space
And Time

Outside of "here"
I suspect there may be
Only Light

1 John 1:5
 
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A_Thinker

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Is the absolute center of a spinning object moving or stationary?

I was hoping to find more info online about this than I did. Does anyone know? Is there a better way to frame the question in order to get better search results?
Everything moves. Ever watch a spinning top move across a table-top ?

A more feasible statement would be that the relative motion of the center ... to the remainder of the object ... might approach 0 delta ...
 
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Petros2015

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This...
Was pretty interesting...
I saw something related to it a little while ago but didn't "get it"


It's definitely a different way of thinking about things than I am used to
But starting to make a bit of sense now
 
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2PhiloVoid

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Is the absolute center of a spinning object moving or stationary?

I was hoping to find more info online about this than I did. Does anyone know? Is there a better way to frame the question in order to get better search results?

... I'm going to go suggest you try the following Google entry "defining movement in the universe."

And here's an entry in relation to physics that came up for me in this search:


I'm sure more can be found than this, obviously, but just for the sake of a simple answer to your question, I'm going to say "moving."

:cool:
 
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essentialsaltes

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I think it may depend on what one means by an "absolute center". If one means a dimensionless point that would be the center of the center of center ad infinitum, then I don't what it means for it to have motion. If one means a part of the object that is "effectively" the center, then I don't know what it means for it to be "part of the spinning object" and not spin.

This is largely my take as well. If we're talking about a geometric point, motion doesn't have much meaning. If we mean a chunk of stuff, some of the bits of the chunk will be moving.

Possibly a better way to think about it is that a small symmetrical mass 'at the center' (or along the axis of rotation) has no linear momentum, but it would have angular momentum due to the spin.

If you stand at the equator, you're moving 1000 miles per hour to the east (with respect to the moon, say).

If you're standing at the north pole, you're not going east at all, but you're slowly rotating in place once a day.
 
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sjastro

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Because the mass increases

You lose the buoyance of the universe
when you try to move that fast and you'll start hydroplaning out of it
Just like if you were in a swimming pool with a friend
and tried to lift your friend out of the water

It's easy at first
But the more you get him out of the water
The heavier and heavier he gets
So the more and more energy is required
When you try to take something with mass
To the speed of light
It appears to get more and more massive
requiring more and more energy
To get up to light speed

An infinite amount to get it to 100%
Because it's effectively become
Infinitely massive
Leaving the buoyancy of Space
And Time

Outside of "here"
I suspect there may be
Only Light

1 John 1:5

You are correct the mass does increase but it is observer dependent, in the object's frame of reference its rest mass remains the same.
Your example doesn’t explain the effect and it requires an analogy with supporting mathematics and a basic knowledge of physics to provide an understanding as to not only why kinetic energy becomes infinite at the speed of light but also the kinetic energies derived for special relativity and Newtonian physics are indistinguishable at low velocities.

Consider a block of stone which has a rest mass m₀ which is initially at rest and pushed so it moves with a velocity u.
You are doing work in moving the block.

According to Newtonian physics the kinetic energy K is defined as the work done by an external force F in moving the block some distance dx.
In this case the rest mass m₀ is a constant.

The Newtonian work-energy equation is;

kinetic1.gif


In special relativity the relativistic mass m as opposed to the rest mass mₒ is not a constant and varies as a function of velocity since it is observer dependent.

kinetic2.gif


Since m is a function of velocity we use the relativistic mass equation which defines the relationship between the relativistic and rest masses;

kinetic3.gif


Taking differentials in the equation gives;

kinetic5.gif


Substituting this relationship back into the previous integral equation for K gives;

kinetic6.gif


The kinetic energy K for special relativity is therefore;

kinetic7.gif


Note in this equation if u = c, the kinetic energy becomes infinitely large.
If u/c << 1 which is the case for low velocities the kinetic energy equation for special relativity reduces to the Newtonian equation using the binomial expansion and approximation (1+x)ⁿ ≈ (1+nx) where x is small.

kinetic10.jpg


(Taking only the first two terms in the bracket since (u/c)⁴ ≈ 0)

The differences between the special relativity and Newtonian equations for kinetic energy when graphed;

kinetic_graph.jpg
 
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durangodawood

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At some point, the disk itself breaks down...
Turning and turning in the widening gyre
The falcon cannot hear the falconer;
Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world,
 
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durangodawood

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Is the absolute center of a spinning object moving or stationary?

I was hoping to find more info online about this than I did. Does anyone know? Is there a better way to frame the question in order to get better search results?
The absolute center is a point of 0 x,y,z size.

A point has no orientation in space, right? So it makes no sense to talk about it rotating.
 
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