Author Topic: Change of Center of Momentum of a system  (Read 13220 times)

Offline bc

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Change of Center of Momentum of a system
« on: 04/02/2020 03:39 pm »
In various past posts here I've seen comments about so called "reactionless drives" and such, and I have a question (I'm a skeptic, but I enjoy these thought experiments).

Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position?

That is to say, the system starts at rest in space (relative to some fixed point), has zero initial momentum, but moves it's internals or rearranges it's parts very quickly, such that the center of mass moves (relative to said point), before returning to it's original position and settling again at rest with no momentum. I understand that the system cannot gain net momentum, but could it do something like the above but where the net forces/momentum (after internal movement/rearrangement) are conserved?

Thanks for your help.
« Last Edit: 12/05/2020 08:21 am by zubenelgenubi »

Offline mrflora

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Re: Change of COM of a system
« Reply #1 on: 04/03/2020 12:31 am »
Swimming through spacetime:

https://groups.csail.mit.edu/mac/users/wisdom/swimming.pdf

Regards,
M.R.F.

Offline meberbs

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Re: Change of COM of a system
« Reply #2 on: 04/14/2020 05:15 am »
The simple answer is no. It is fundamentally disallowed by physics.

The swimming through spacetime above is a real thing, but it relies on the curvature of spacetime, which would be caused by being in the gravitational field of another object, plus the motions themselves would be able to emit gravitational waves (tiny ones, but the motion itself is inconceivably small in a practical situation.) Therefore it can't be considered a closed system. It is comparable to how you can push off the Earth's magnetic field in LEO. Relatively easy to calculate how much force you get, but requires more careful work to show where the balancing force goes.

Offline Josave

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Re: Change of COM of a system
« Reply #3 on: 09/10/2020 10:06 am »
Please, consider these attached pulbications about permanently removng momentum from a system. It is allowed by General Relativity.

The emission of gravitational waves (from a quadrupole source) permanently moves the source. This has been proved by astrophysical observations. The Einstein therory allows gravitational waves to carry linear momentum away from the source, in a flat spacetime, no swimming in curved spacetime.

More information in the concept of "linear frame dragging", another way of removing linear momentum from an isolated system...

The effect is tiny, but can be increased with future technology. In the above references, it is estimated to be on the order of 1/c6. After a quick peek in the formulas, to be useful for a practical rocket, the effect that can be defined as a "quadrupole rotating engine" must have a big mass or rotate such fast that centripetal accelerations must be of 1024 m/s2

A big technical challenge!


« Last Edit: 09/10/2020 10:12 am by Josave »

Offline trm14

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Re: Change of COM of a system
« Reply #4 on: 09/10/2020 12:05 pm »
Please, consider these attached pulbications about permanently removng momentum from a system. It is allowed by General Relativity.

The emission of gravitational waves (from a quadrupole source) permanently moves the source. This has been proved by astrophysical observations. The Einstein therory allows gravitational waves to carry linear momentum away from the source, in a flat spacetime, no swimming in curved spacetime.

More information in the concept of "linear frame dragging", another way of removing linear momentum from an isolated system...

The effect is tiny, but can be increased with future technology. In the above references, it is estimated to be on the order of 1/c6. After a quick peek in the formulas, to be useful for a practical rocket, the effect that can be defined as a "quadrupole rotating engine" must have a big mass or rotate such fast that centripetal accelerations must be of 1024 m/s2

A big technical challenge!

In what sense would this be better than a photon rocket?

Offline 1

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Re: Change of COM of a system
« Reply #5 on: 09/10/2020 03:00 pm »
The simple answer is no. It is fundamentally disallowed by physics.

The swimming through spacetime above is a real thing, but it relies on the curvature of spacetime, which would be caused by being in the gravitational field of another object, plus the motions themselves would be able to emit gravitational waves (tiny ones, but the motion itself is inconceivably small in a practical situation.) Therefore it can't be considered a closed system. It is comparable to how you can push off the Earth's magnetic field in LEO. Relatively easy to calculate how much force you get, but requires more careful work to show where the balancing force goes.

Just to add to this, in that center of mass actually has no appreciable meaning in relativity, because mass by itself can no longer be considered an immutable, conserved quantity. E=mc2 and all that.

The analogous concept in relativity is center of momentum. Rather than correspond to a physical place, as center of mass implies, center of momentum corresponds to a reference frame in which the relative momenta of all components of a system sum to zero. This is a more encompassing formulation, as it takes into account momentum carried by massless particles. With the ability to do that, even an object 'swimming in spacetime' becomes well behaved, because the emission of gravitational waves balances the shift of the emitting object.

In what sense would this be better than a photon rocket?

It wouldn't be, for the exact same reasons. A photon rocket is another system where the center of mass flies off in one direction, but the center of momentum stays put. Note that the center of mass-energy also stays put, but mass by itself no longer tells the entire story, so to speak.

Offline Josave

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Re: Change of COM of a system
« Reply #6 on: 09/10/2020 08:11 pm »
In what sense would this be better than a photon rocket?

Thanks for your interest in this subject.

I have done a fast reading of Bonnor articles and seems that the gravitational wave rocket expels no energy other than the inherent of the gravitational wave itself. In this sense is better than the photon rocket, that expels only 1/c momentum unit for each energy unit expelled. According to Cooperstock (1967) Phys. Rev 165 1424 "Since this is the same orfer in c as the energy flux, it appears that the momentum flux can, in certain circumstances, play as significant a role as the energy flux".

Here I will ask for help of forum members, since GR is a difficult theory and hard to non experts like me. More discussion about if the gravitational waves carry or not energy are in the attached article... to discuss if gravitational waves are energy or just distorsion of spacetime.

But the gravitational wave rocket can be interesting for several practical engineering reasons (this is speculative):

  -No need to convert directly mass to energy. Foreseable technology for photon rockets are nuclear reactions, with inherent difficulty to focus the photon beam in the desired direction.

  -The quadrupole gravitational wave is easily focused in the spinning axis of a rotating quadrupole mass configuration.

  -The gravitational emmision mechanism is "cold", of course if engineered in some way like using high speed rotating graphene nano-rods or fast rotating electrons clouds arranged in a non-raditation configuration to avoid sincrotron losses.

Summarizing, the 2018 Bonnor reprint of his 1997 article deserves attention, maybe it can give us the clue to an efficient mechanism to radiate linear momentum against the flat spacetime, in a much efficient way that the photon rocket.
« Last Edit: 09/10/2020 08:16 pm by Josave »

Offline Reactionless2020

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Re: Change of COM of a system
« Reply #7 on: 09/11/2020 09:47 pm »
There is no chance any kind of reactionless drive or warp drive or em drive or vacuum thruster ever to work if Newton's 3rd law holds always and everywhere in the direction of the expected acceleration.

In a few words, from the moment the above aspect is not addressed by all those proposals, propellantless propulsion is nonsense except....

Offline Redclaws

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Re: Change of COM of a system
« Reply #8 on: 09/11/2020 10:21 pm »
There is no chance any kind of reactionless drive or warp drive or em drive or vacuum thruster ever to work if Newton's 3rd law holds always and everywhere in the direction of the expected acceleration.

In a few words, from the moment the above aspect is not addressed by all those proposals, propellantless propulsion is nonsense except....
It’s worth noting this is wrong about, for example, the Alcubierre warp drive.  Entirely.

Not that we can make it work or anything like that, but it doesn’t violate Newton’s third law.  Warp concepts in general would not.
« Last Edit: 09/11/2020 10:22 pm by Redclaws »

Offline Reactionless2020

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Re: Change of COM of a system
« Reply #9 on: 09/11/2020 10:36 pm »
It’s worth noting this is wrong about, for example, the Alcubierre warp drive.  Entirely.

Not that we can make it work or anything like that, but it doesn’t violate Newton’s third law.  Warp concepts in general would not.

I think I was misunderstood. If any theory including Alcubierre's warp drive cannot violate (or better extend) Newton's 3rd law then this theory is automatically wrong and cannot work. From the moment the warp drive respects Newton's 3rd law then it will never work.

Certainly  there is a solution...

Offline Redclaws

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Re: Change of COM of a system
« Reply #10 on: 09/11/2020 10:39 pm »
You’re just repeating yourself.

Alcubierre’s drive concept relies on warping space.  That facet of it does not involve reactionless movement, because it doesn’t involve movement in that sense.

Offline Reactionless2020

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Re: Change of COM of a system
« Reply #11 on: 09/12/2020 07:27 am »
You’re just repeating yourself.

Alcubierre’s drive concept relies on warping space.  That facet of it does not involve reactionless movement, because it doesn’t involve movement in that sense.

Yes, you are right, however there still things that do not fit even if it is mathematically correct (I will expand on this later on the other thread). Regarding the reactionless movement concepts, I suppose you agree with me.

Offline meberbs

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Re: Change of COM of a system
« Reply #12 on: 10/29/2020 12:01 am »
I have done a fast reading of Bonnor articles and seems that the gravitational wave rocket expels no energy other than the inherent of the gravitational wave itself. In this sense is better than the photon rocket, that expels only 1/c momentum unit for each energy unit expelled. According to Cooperstock (1967) Phys. Rev 165 1424 "Since this is the same orfer in c as the energy flux, it appears that the momentum flux can, in certain circumstances, play as significant a role as the energy flux".
You seem to have missed that the statement "expels no energy other than the energy of the [] wave itself" applies equally well to both EM waves (photons) and gravitational waves. Both cases have the 1/c ratio of momentum to energy. (Your source seems to have made a serious mistake in calculation, as he says "This is larger than the momentum loss calculated by other researchers for different sources by a factor of c." Other researchers are right, he literally must be wrong, because he has the wrong units, a momentum/energy ratio must have units of inverse velocity, so his expression missing the factor of c would be unit-less and therefore wrong.)

This means that all of your other claimed benefits of gravitational waves fail to exist. Even if there was a way to generate high power directed gravitational waves (we don't know of one), it would still need a power source such as a matter-antimatter reactor that could consume a significant fraction of the mass of the vehicle into raw energy to power the drive.

Offline JohnFornaro

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Re: Change of COM of a system
« Reply #13 on: 10/29/2020 12:23 pm »
... it would still need a power source such as a matter-antimatter reactor that could consume a significant fraction of the mass of the vehicle into raw energy to power the drive.

Not sure if this is the place to bring this up, but... In the various discussions of EM drive, there doesn't seem to be any explanation of where the power comes from to operate the drive.
Sometimes I just flat out don't get it.

Offline hfgw

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Re: Change of COM of a system
« Reply #14 on: 12/02/2020 01:38 pm »
A space propulsion system must directionally emit hot gases or ions or debris, or photon rocked radiation to be able to move. Momentum is conserved and no external massive universe is needed to allow this "conservation" (for a truly alone crew..).
If an attractive field is produced outside the spacecraft it will affect the spacecraft and all the masses of the universe. Momentum is conserved in agreement with this consideration.  If there were no outside universe it would work differently, or would not work at all, but the outside universe exists.
Clearly a transient attractive field will apply transient acceleration in the above sense and the spacecraft will gain speed.
Now we have to find a directionally emitted oscillating radiation field that as soon as it is rectified it will produce an attractive unipolar field outside and near the spacecraft. After solving the technical problems, we already know that  spacetime itself can do that rectification for a well known kind of really existing waves.
« Last Edit: 12/03/2020 04:44 pm by hfgw »

Offline OnlyMe

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Re: Change of COM of a system
« Reply #15 on: 12/03/2020 05:45 pm »
In various past posts here I've seen comments about so called "reactionless drives" and such, and I have a question (I'm a skeptic, but I enjoy these thought experiments).

Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position?

That is to say, the system starts at rest in space (relative to some fixed point), has zero initial momentum, but moves it's internals or rearranges it's parts very quickly, such that the center of mass moves (relative to said point), before returning to it's original position and settling again at rest with no momentum. I understand that the system cannot gain net momentum, but could it do something like the above but where the net forces/momentum (after internal movement/rearrangement) are conserved?

Thanks for your help.

It seems to me your initial question centers on whether any action in a closed system, can result in a change or changes of momentum when viewed from outside the closed system...?

Most of the answers whenever a question like this is raised is no, with a reference to COM.

Reality is not so easy today as it was some 350+ years ago, when the basis for COM as we know it today were laid down.

Take a simple cell phone. Set it to airplane mode to cut off all EM interaction with the larger environment. First does the cell phone and what occurs electrically and mechanically inside, while it is in airplane mode, represent a closed system?... Obviously everything that occurs within that closed system does in fact obey COM. Now consider setting a cell phone alarm to vibrate. That vibration, while it originates from within the closed system, is in fact observable from outside the closed system.

There are other examples of devices, even natural closed system examples, that could fall within the conditions set in your OP. None violate COM from within or from outside. And yes if you get far into the weeds arguments can be made that suggest these are not truly closed systems, but they become discussions of technical fine lines. The point I was attempting to make is that once you set a cell phone to airplane mode and have set an internally defined and controlled alarm, the vibrating alarm originates from within a closed system, even while it can be observed, and affect the environment outside that closed system.

And no a cell phone is not going to become a propulsion system for a satellite. It will just jiggle back and forth.

I can imagine one closed system mechanism that might produce a very small, perhaps even useable vector force. But that is a far more complex discussion and not immediately relative to this discussion.

« Last Edit: 12/03/2020 05:48 pm by OnlyMe »

Offline edzieba

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Re: Change of COM of a system
« Reply #16 on: 12/04/2020 08:31 am »
All you've done there is defined a closed system incorrectly. If it is interreacting with something 'outside' the system (and observation is itself an interaction, both in the quantum sense and in the classical shooting-photons-at-an-object-and-watching-where-they-bounce sense) then you no longer have a closed system.
To take the 'phone in airplane mode' example: the phone is emitting EM radiation due to being hot. The phone is in contact with ambient air and driving air circulation (convection). If the screen is on then it will be emitting further higher frequency EM. If it is on a table, it is heating the table through conduction. The phone has mass, so is attracting the Earth upwards slightly (as well as slightly attracting all objects nearby towards it ever so very slightly), and is also being attracted by the Earth. A truly closed system must include ALL these interactions.

Offline hfgw

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Re: Change of COM of a system
« Reply #17 on: 12/04/2020 09:22 am »
I have done a fast reading of Bonnor articles and seems that the gravitational wave rocket expels no energy other than the inherent of the gravitational wave itself. In this sense is better than the photon rocket, that expels only 1/c momentum unit for each energy unit expelled. According to Cooperstock (1967) Phys. Rev 165 1424 "Since this is the same orfer in c as the energy flux, it appears that the momentum flux can, in certain circumstances, play as significant a role as the energy flux".
You seem to have missed that the statement "expels no energy other than the energy of the [] wave itself" applies equally well to both EM waves (photons) and gravitational waves. Both cases have the 1/c ratio of momentum to energy. (Your source seems to have made a serious mistake in calculation, as he says "This is larger than the momentum loss calculated by other researchers for different sources by a factor of c." Other researchers are right, he literally must be wrong, because he has the wrong units, a momentum/energy ratio must have units of inverse velocity, so his expression missing the factor of c would be unit-less and therefore wrong.)


They are using Plank units

https://en.wikipedia.org/wiki/Planck_units

Offline OnlyMe

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Re: Change of COM of a system
« Reply #18 on: 12/04/2020 02:10 pm »
All you've done there is defined a closed system incorrectly. If it is interreacting with something 'outside' the system (and observation is itself an interaction, both in the quantum sense and in the classical shooting-photons-at-an-object-and-watching-where-they-bounce sense) then you no longer have a closed system.
To take the 'phone in airplane mode' example: the phone is emitting EM radiation due to being hot. The phone is in contact with ambient air and driving air circulation (convection). If the screen is on then it will be emitting further higher frequency EM. If it is on a table, it is heating the table through conduction. The phone has mass, so is attracting the Earth upwards slightly (as well as slightly attracting all objects nearby towards it ever so very slightly), and is also being attracted by the Earth. A truly closed system must include ALL these interactions.

As I said, “ And yes if you get far into the weeds arguments can be made that suggest these are not truly closed systems, but they become discussions of technical fine lines.”.

All you have done is assert that there are no closed systems!

Strip away all but a timed alarm set to vibrate. Drop it into earth’s shadow in the vacuum of space. Make it a spring wound alarm... and yes you can still argue it is not entirely separated from the universe and so not a closed system. But most of your objections to the cell phone would have been eliminated and yet it will still jiggle when the alarm goes off.

My intent was a response to the OP, that asked about a closed system creating momentum internally, observable  externally, even should that momentum/motion just be jiggling back and forth. (My words restating the ask in the OP.)

But yes, there are no truly closed systems. The point I was attempting to make is that yes you can design a mechanism that “jiggles” without pushing on anything outside of itself.

Now, going further into the weeds, we would have to drive the discussion into explaining exactly what inertia and gravitation are, because the mechanics of the vibrating device, ultimately depends on at least inertia and depending on proximity gravitation. But those discussions have no current resolution, for while we can describe the mechanics of each with great detail, there is little or no consensus view describing the mechanism(s) of either.

Offline edzieba

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Re: Change of COM of a system
« Reply #19 on: 12/04/2020 02:58 pm »
A system that 'jiggles' is performing zero shifting of it's CoM and has zero momentum. It will only gain any momentum if one of it's jiggles hits another object, and now... you need to include that object in your closed system, and have simply created a crude reation drive.

And if you want to start positing mysterious reactionless drives then you need to be VERY careful about ensuring you have gone down sufficiently 'in the weeds' before declaring you've discovered an effect!

Offline zubenelgenubi

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Re: Change of COM of a system
« Reply #20 on: 12/04/2020 10:14 pm »
I have done a fast reading of Bonnor articles and seems that the gravitational wave rocket expels no energy other than the inherent of the gravitational wave itself. In this sense is better than the photon rocket, that expels only 1/c momentum unit for each energy unit expelled. According to Cooperstock (1967) Phys. Rev 165 1424 "Since this is the same orfer in c as the energy flux, it appears that the momentum flux can, in certain circumstances, play as significant a role as the energy flux".
You seem to have missed that the statement "expels no energy other than the energy of the [] wave itself" applies equally well to both EM waves (photons) and gravitational waves. Both cases have the 1/c ratio of momentum to energy. (Your source seems to have made a serious mistake in calculation, as he says "This is larger than the momentum loss calculated by other researchers for different sources by a factor of c." Other researchers are right, he literally must be wrong, because he has the wrong units, a momentum/energy ratio must have units of inverse velocity, so his expression missing the factor of c would be unit-less and therefore wrong.)
They are using Planck units
https://en.wikipedia.org/wiki/Planck_units

Member: What do Planck units have to do with the above?
Quote
In particle physics and physical cosmology, Planck units are a set of units of measurement defined exclusively in terms of four universal physical constants, in such a manner that these physical constants take on the numerical value of 1 when expressed in terms of these units.

The four universal constants that, by definition, have a numeric value 1 when expressed in these units are:
the speed of light in a vacuum, c,
the gravitational constant, G,
the reduced Planck constant, ħ,
the Boltzmann constant, kB.
« Last Edit: 12/04/2020 10:18 pm by zubenelgenubi »
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Offline OnlyMe

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Re: Change of COM of a system
« Reply #21 on: 12/04/2020 11:36 pm »

A system that 'jiggles' is performing zero shifting of it's CoM and has zero momentum. It will only gain any momentum if one of it's jiggles hits another object, and now... you need to include that object in your closed system, and have simply created a crude reation drive.

And if you want to start positing mysterious reactionless drives then you need to be VERY careful about ensuring you have gone down sufficiently 'in the weeds' before declaring you've discovered an effect!

This began just as a response to the following sentence from the OP,  “ Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position? ”

Forget the cell phone I used it as an example only because mine is on vibrate and I had just received a call. And forget reactionless drives. The example was only to address that single sentence in the OP.

Even so... your above statement is wrong, when you assert that the center of mass does not change. It is the changing center of mass that causes the “jiggle”, or vibration.

From Wiki, “ A vibrator is a mechanical device to generate vibrations. The vibration is often generated by an electric motor with an unbalanced mass on its driveshaft. ... Typically, they are components of larger products such as smartphones, pagers, vibrating sex toys, or video game controllers with a "rumble" feature.”

Note that bit about the unbalance drive shaft, leading to a changing center of mass and vibration.

Technically no system I can think of is truly entirely closed! But as far as a vibrator is concerned, drop it out an airlock into the vacuum of space and as far as the vibrating mechanism is concerned it is close to closed. And it is the changing center of mass that causes the vibration.

Offline 1

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Re: Change of COM of a system
« Reply #22 on: 12/05/2020 12:46 am »
Even so... your above statement is wrong, when you assert that the center of mass does not change. It is the changing center of mass that causes the “jiggle”, or vibration.

No. Wikipedia says 'unbalanced mass', not center of mass. No one else is saying center of mass. Those are only your words.

In the vibrator, a shift in internal mass is countered by an opposite shift in external mass. Were you to drop one out the airlock in space, you'd actually find that the outer casing enclosing the motor would begin to rotate in the opposite direction of the drive shaft. The center of mass, of all components, remains unchanged.

Back here on Earth, the vibrator attempts to spin as well; but is prevented from doing so by the person or test bench holding it in place. This actually transmits the torque from the spinup of the motor to the ground; and ultimately the Earth itself must be considered part of your system. This forum (and others) are very much flooded with ideas from people who have neglected that.

edzeiba is correct. You've not gone sufficiently deep into the weeds.

This began just as a response to the following sentence from the OP,  “ Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position? ”

This was correctly answered by meberbs as 'no' with a ', but...' .

Offline OnlyMe

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Re: Change of COM of a system
« Reply #23 on: 12/05/2020 06:32 am »
Even so... your above statement is wrong, when you assert that the center of mass does not change. It is the changing center of mass that causes the “jiggle”, or vibration.

No. Wikipedia says 'unbalanced mass', not center of mass. No one else is saying center of mass. Those are only your words.

In the vibrator, a shift in internal mass is countered by an opposite shift in external mass. Were you to drop one out the airlock in space, you'd actually find that the outer casing enclosing the motor would begin to rotate in the opposite direction of the drive shaft. The center of mass, of all components, remains unchanged.

Back here on Earth, the vibrator attempts to spin as well; but is prevented from doing so by the person or test bench holding it in place. This actually transmits the torque from the spinup of the motor to the ground; and ultimately the Earth itself must be considered part of your system. This forum (and others) are very much flooded with ideas from people who have neglected that.

edzeiba is correct. You've not gone sufficiently deep into the weeds.

This began just as a response to the following sentence from the OP,  “ Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position? ”

This was correctly answered by meberbs as 'no' with a ', but...' .

I have no issue with meberbs response. I also don’t see anywhere he added any ‘, but...” to his statement. Point it out more clearly if I missed something. I understood his post to be focus more toward the COM issue.

There was and is no COM issue, as far as I can tell in the workings of a vibrator and whether in its simplest form, the internal mechanics could be considered a closed system and yet have some affect beyond the confines of the device itself, without violating COM.

When you spin an unbalanced mass, the center of mass moves with the imbalance. Stop the spinning unbalanced mass at several different points and the center of mass of the system as a whole will have changed. And while it spins there is momentum involved, both in the spin and the out of balance vibrations.

This really should not have been so complicated and is not worth further energy.


Offline 1

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Re: Change of COM of a system
« Reply #24 on: 12/05/2020 07:40 am »
I also don’t see anywhere he added any ‘, but...” to his statement. Point it out more clearly if I missed something.

The 'but' comes from his touching on an object swimming in spacetime; and mentioning the emission of gravitational waves that necessarily accompany that. Classically, that situation would appear to be a COM shift. However, since mass and energy have an explicit equivalency in relativity, proper formulation in modern physics requires taking both mass and energy into account, not just or the other.

There was and is no COM issue, as far as I can tell in the workings of a vibrator and whether in its simplest form, the internal mechanics could be considered a closed system

When you spin an unbalanced mass, the center of mass moves with the imbalance. Stop the spinning unbalanced mass at several different points and the center of mass of the system as a whole will have changed. And while it spins there is momentum involved, both in the spin and the out of balance vibrations.

This really should not have been so complicated and is not worth further energy.

All completely wrong. When you spin an unbalanced mass, you move opposite to the imbalance. The center of mass of you and the spinning object remains unchanged. You continue to focus on the object being spun, and continue to ignore the object causing the spin. This demonstrates a fundamental misunderstanding of classical mechanics on your part. Nothing you describe can be considered a closed system.

Offline zubenelgenubi

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Re: Change of COM of a system
« Reply #25 on: 12/05/2020 08:17 am »
This thread's discussion is no longer progressing.  Several members are answering the member's questions, but I perceive that they are not being listened to.

Further private discussion, if desired, can be accomplished via Personal Messaging (cartoon speech bubble icon).

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« Last Edit: 12/05/2020 08:18 am by zubenelgenubi »
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