# Does a spinning disk gain relativistic mass

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Does previous post sound a little bit like a joke?

Here's yet another way to transfer energy from a moving battery: Laser device attachet to the battery. With this energy transfer method it's clear that there exist a thrust effect and redshifft effect.

Do you violate conservation of momentum with this?

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A) If you have a closed system with 2 disks and spin the disks in opposite directions, would the system stay at rest in an inertial frame?

B) And if you tilted the disks would the system still stay at rest in an inertial frame?

C) Is relativistic mass directional?

If A then you could change the center of mass of a system while keeping the system at rest in an inertial frame.

If (B and C) The same thing.

So if A and/or (B and C), then I believe that a closed system could accelerate itself.

Edited by 514void
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Do you violate conservation of momentum with this?

No. I guess. As Strange said, amusing energy juggling gadgets are almost like ordinary matter bouncing apparatuses.

If you have a closed system with 2 disks and spin the disks in opposite directions, would the system stay at rest in an inertial frame?

Yes. Very very very likely the center of mass would stay at rest.

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Yes, but if you have these disks on the top of a container, and the center of mass of the system is not at the center of mass of the 2 disks, then would the center of mass move towards the disks as they were spun up due to relativistic mass gain?

would the system move so that the center of mass stayed at rest in an inertial frame?

would transferring energy from one part to another part using AC power cause acceleration?

Edited by 514void
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514void, I don't know what part of this you don't get: you can't move things around in a closed system to change its net momentum.

This is like designs for perpetual motion machines: it doesn't matter how complicated you make it or how many weights, wheel, pulleys, levers, buckets, etc. you add, the answer is still no.

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Relativity seems to allow it.

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Relativity seems to allow it.

Only because you aren't accounting for all of the energy present in the system

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Was just thinking that transferring the spin from a disk from the bottom of a container to spin a disk on the top of the container using AC current, how would the system know which way to move to keep the center of mass at rest in an inertial frame.

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Relativity seems to allow it.

You are just moving energy backwards and forwards, which has exactly the same effect as moving mass backwards and forwards.

Was just thinking that transferring the spin from a disk from the bottom of a container to spin a disk on the top of the container using AC current, how would the system know which way to move to keep the center of mass at rest in an inertial frame.

And using AC to power it makes no difference at all. An AC motor would use exactly the same amount of energy as a DC motor used to spin your wheel up to the same amount.

Edited by Strange
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Was just thinking that transferring the spin from a disk from the bottom of a container to spin a disk on the top of the container using AC current, how would the system know which way to move to keep the center of mass at rest in an inertial frame.

AC current, well there are some propagating electromagnetic fields carrying energy and momentum, not really different from a laser.

DC current? Now we have some kind of ion thruster.

Well how about a drive shaft then? Probably when you press a brake pad on a spinning drive shaft, the shaft will try to move to some direction, the direction opposite to the energy flow.

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You are just moving energy backwards and forwards, which has exactly the same effect as moving mass backwards and forwards.

And using AC to power it makes no difference at all. An AC motor would use exactly the same amount of energy as a DC motor used to spin your wheel up to the same amount.

So moving energy from one spinning disk from one side of a container to another using AC current would move the system to keep the center of mass at rest in an inertial frame?

you could get really high acceleration with that system, just have the container really long.

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So moving energy from one spinning disk from one side of a container to another using AC current would move the system to keep the center of mass at rest in an inertial frame?

you could get really high acceleration with that system, just have the container really long.

Or you could just move a large mass from one end to the other and get the same result, and not waste nearly as much energy.

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you couldn't move the center of mass faster than the speed of light that way.

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you couldn't move the center of mass faster than the speed of light that way.

As opposed to which method where this is possible?

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So moving energy from one spinning disk from one side of a container to another using AC current would move the system to keep the center of mass at rest in an inertial frame?

you could get really high acceleration with that system, just have the container really long.

Assume for simplicity, that the spinning disk (or bowling ball or whatever you use) has half the mass of the container. If you move it from one end of the container to the other, the container will move half that distance in the other direction. That's it. Done.

Now you want to move the mass back to the starting position so you can do it again. Guess what: the container will move back to where it was. It makes no difference whether you do this with spinning disks, AC or DC motors, bowling balls, jets of water, or buckets of jellyfish. You are simply moving backwards and forwards and not going anywhere.

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the method where you spin a disk in a system to move the center of mass, and according to strange, the system would move to keep the center of mass at rest in an inertial frame.

If the disk was far enough away from the center of mass, then as you spin it up, the center of mass would move toward the disk faster than the speed of light.

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If the disk was far enough away from the center of mass, then as you spin it up, the center of mass would move toward the disk faster than the speed of light.

Of course it wouldn't. Why would you think that? You can only move the disk at less than the speed of light and so the container will only shift in the opposite direction at less than the speed of light.

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Assume for simplicity, that the spinning disk (or bowling ball or whatever you use) has half the mass of the container. If you move it from one end of the container to the other, the container will move half that distance in the other direction. That's it. Done.

Now you want to move the mass back to the starting position so you can do it again. Guess what: the container will move back to where it was. It makes no difference whether you do this with spinning disks, AC or DC motors, bowling balls, jets of water, or buckets of jellyfish. You are simply moving backwards and forwards and not going anywhere.

Nice simplification, I think you assume relativistic mass is imaginary.

Of course it wouldn't. Why would you think that? You can only move the disk at less than the speed of light and so the container will only shift in the opposite direction at less than the speed of light.

umm, if you spin the disk up at any acceleration, it will gain some relativistic mass, and the center of mass would move in the system. If the system was long enough, then the center of mass could move faster than the speed of light, even if the spin of the disk was quite small.

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Nice simplification, I think you assume relativistic mass is imaginary.

No, I assume mass-energy behaves like, well, mass-energy. You seem to assume that it has magical powers.

umm, if you spin the disk up at any acceleration, it will gain some relativistic mass, and the center of mass would move in the system. If the system was long enough, then the center of mass could move faster than the speed of light, even if the spin of the disk was quite small.

I don't see why you think the length of the system makes any difference. You are simply moving mass (energy) from one place (the power source) to another (the wheel). You could do this more easily by chasing an elephant from one end to the other. However you do it, this movement of mass will (must) will take place at less than the speed of light and so the center of mass will move at less than the speed of light.

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!

Moderator Note

Moved to Speculations.

The problems with the notion have been pointed out enough times. The spinning disc question was interesting and illuminating but this insistence of FTL in the face of good argument is too speculative for the main forum

Do not respond to this modnote in the thread.

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i realise that moving faster than light is impossible, so therfore I assume that moving the center of mass by spinning a disk will NOT move the system.

but if you can change the center of mass in a system without actually moving it, then you could use this to accelerate the system.

for example, if you moved the center of mass to the top of a system without moving it, then you could move masses in the system to move the system upwards.

This could be used to accelerate the system.

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Nice simplification, I think you assume relativistic mass is imaginary.

umm, if you spin the disk up at any acceleration, it will gain some relativistic mass, and the center of mass would move in the system. If the system was long enough, then the center of mass could move faster than the speed of light, even if the spin of the disk was quite small.

once again: it is not sufficient to just claim this (writing the statement is easy). You need to show that this is true with physics equations.

i realise that moving faster than light is impossible, so therfore I assume that moving the center of mass by spinning a disk will NOT move the system.

but if you can change the center of mass in a system without actually moving it, then you could use this to accelerate the system.

for example, if you moved the center of mass to the top of a system without moving it, then you could move masses in the system to move the system upwards.

This could be used to accelerate the system.

Moving mass around internally moves one mass relative to another, e.g. the internal mass relative to the container's. The center of mass of the whole system doesn't move, and the container's motion stops when the internal mass reaches the end of the container.

There is no acceleration of the center of mass with your proposal.

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So moving a spinning disk with some relativistic mass gain takes the same amount of force as moving the same disk that isn't spinning?

I would of thought it would require more force.

And this force difference could be used to accelerate a system.

Wherever the center of mass is seems secondary.

And spinning a disk faster or slower would not speed it up or slow it down relative to any inertial frame, unless you assume a preferred frame for it to gain or lose momentum relative to.

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So moving a spinning disk with some relativistic mass gain takes the same amount of force as moving the same disk that isn't spinning?

I would of thought it would require more force.

Classically F=ma; more mass requires a larger force for the same acceleration, but "accelerate" and "move" are not the same thing, and I'm not sure what connection this has to your proposed reactionless propulsion.

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Phase 1 The spinning disk is moving downwards in a container, its spin is slowed to a stop.

Phase 2 The disk is accelerated upwards with a force, it slows and starts moving upwards.

Phase 3 The disk is spun up giving it more relativistic mass.

Phase 4 The disk is accelerated downwards with a force, it slows and starts moving downwards.

So Phase 2 would accelerate the system downwards, and Phase 4 would accelerate the system upwards.

Phase 4 would need more force than Phase 2, That would make the system accelerate.

I don't see how Phase 1 and Phase 3 would make any difference.

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