Linear momentum conservation puzzle

Discussion in 'Physics & Math' started by Q-reeus, Nov 13, 2016.

  1. danshawen Valued Senior Member

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    Okay. My machinery is dead then. Whatever that means.
     
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  3. Q-reeus Valued Senior Member

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    Never heard of colloquialisms like 'the motor just died', 'the motor's dead', etc.? You might be surprised how many folks are familiar with such. No need to answer this one Dan.
     
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  5. The God Valued Senior Member

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    This common sense seems to have become very 'uncommon' for all except Q-reeus.
     
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  7. Q-reeus Valued Senior Member

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    Not my fault. Set out a clearly defined scenario in #1, pointed out the apparent dilemma it generated, and have given all the necessary clarifications and clues needed to solve it. Hell, with so many ideas being tossed up and eliminated along the way, one would expect someone should by now have figured it. As remarked before, none of those accusing me of being 'anti-science' in another thread have shown the balls or nous to front up here. Pleasing in a way.

    It's commendable that you and others have risked failure and at least tried. With no sign of anyone converging towards the actual answer, I'll wait for at least OceanBreeze to come back, and may wrap it up shortly thereafter. If I'm still around that is. Deeply pissed off with how imo this place morally malfunctions at all levels.
     
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  8. OceanBreeze Registered Member

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    Thank you for extending me that courtesy.

    I’m still working on a solution employing a Lorentz transform, but I am not clear on what needs to be transformed? Since you say photons are not involved, and I don’t see anything mechanical moving at relativistic speeds, that only leaves the transferred mass (or the momentum of said mass) as the candidate for the transform.

    Can you let me know if that is right; that the Lorentz transform applies to the transferred mass or the momentum associated with it?
     
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  9. Q-reeus Valued Senior Member

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    It doesn't sound right to me. However, my advice is just go ahead and present your proposal in as clear a fashion as possible. Make sure to define carefully any terms and vector or tensor relationships wrt key geometric features in the system given. Good luck!
     
  10. The God Valued Senior Member

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    Come on, man; Ocean Breeze has clearly stated that he does not know what is to be transformed! You know what it means.

    I would suggest you retype the riddle in a new post, now it has become #1, #29, #39, #55, #105 etc etc. Make a single post with all your bones for dogs then give tight 24 hrs and if no correct response post the solution. I will urge Mods not to ban you till then, I am not aware if your case is so bad in some other thread.
     
  11. danshawen Valued Senior Member

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    You are revealing that friction factors into whatever you are trying to show, which is progress. That's what eventually brings a motor to a stop when it 'dies'. The other cause, neglecting friction, would of course be a dead battery together with frictional losses. The mechanical equivalent of heat is due to friction too, of course.

    So, whatever it was you were trying to convey evidently had to do with these energy losses, yet you also claim is not anything to do with partitioning or 'isolating' parts of the system, which is not even possible without taking into account these mechanical energy losses that are not subject to the usual thought experiment controls, like eliminating them altogether with frictionless bearings and superconducting wires.

    It is entirely possible I have inadvertently eliminated some salient feature about the system that is also important. Can you hint at what you had in mind other than attributing life to some piece of mechanical / electrical equipment as dead as a dynomotor or a battery, or a pair of spinning disks connected by a common axle?? The latter "lifeless" system can easily be made to stop spinning via frictional forces as well, so how is that system any less "alive?'' Let's torque about that.
     
    Last edited: Dec 17, 2016
  12. danshawen Valued Senior Member

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    Never mind how it "dies". How does it "live?" I would agree, things that are alive can move their centers of masses a tiny bit while they remain alive by various processes. What else? My own center of mass (or the center of my arguments, at least) seems not to be able to move. I must be dead. Pity. Seems like only yesterday, my dynomotor would crank easily and my battery was fully charged.

    You never get all of the energy back from a regenerative flywheel, unless it has superconducting bearings. Life on Earth goes on because solar energy keeps powering it. Narrow it down. What exactly interests you about the energy exchange?
     
    Last edited: Dec 17, 2016
  13. Q-reeus Valued Senior Member

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    Sorry, but anyone interested to have followed this thread's meanderings should have picked and retained all the necessary info. Anyway, it won't drag on too much longer.
     
  14. Q-reeus Valued Senior Member

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    Your #119: ". Nope. Finished." If only your latest two posts had any relevant content, Dan, It might have excused breach of that 'commitment'. Alas, no.
     
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  15. danshawen Valued Senior Member

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    OK then. Maybe someone else will stumble on whatever answer you are looking for. Thanks for an interesting thread.
     
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  16. OceanBreeze Registered Member

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    What I like about this sort of thread is the collateral benefits that come from digging around, looking for an answer. One of the interesting things I rediscovered is the Ehrenfest paradox, which I had encountered before but since forgotten about. I came across it again while considering if there is an axial force developed on a shaft due to angular velocity.
    Another strange thing I found when considering whether or not a closed system can cause a translation of mass, is this apparently unsuccessful attempt using gyroscopes.
    So, even if I don’t come up with the answer to this thread*, I have benefitted from participating in it.
    *(But I haven’t given up yet; starting on a different approach)
     
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  17. Q-reeus Valued Senior Member

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    Amusingly perhaps, that effect will give rise in general to tiny stresses in the radial and circumferential directions, but nothing appreciable along the axis. As you probably knew anyhow.
    I well remember his notion of a 'reactionless drive' gaining wide publicity/notoriety back in the mid 1970's. Must have taken me all of 10 minutes to figure out the likely explanation for an actual slight reduction in measured weight when the gyros were precessing about: http://protabletennis.net/content/topspin-and-backspin
    Start at 'Backspin'. His contraption's arrangement and motions iirc matched for that. Not sure if he ever tried placing the whole thing inside a bell-jar, but that's when he would have come back down to earth. Something I didn't know till reading the Wikipedia article on him: https://en.wikipedia.org/wiki/Eric_Laithwaite
    - he was not the originator. Instead a relative unknown by the name of Alex Jones (not the human foghorn by the same name).
    Good for you. Keep trying by all means! Nothing ventured - nothing gained.

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  18. danshawen Valued Senior Member

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    Easy, yes. Nutation is also spin, and produces positive or negative "magnus" buoyancy type forces depending on texture and direction of rotation. 'Isolated', no, unless you include atmosphere as part of your "system". Good one, though.

    A rotor (armature) of a motor, brushless or otherwise, will have a rough texture (for cooling purposes more than anything else), and quite a bit of magnus effect when spinning in air as well as gyroscopic effects including precession and nutation, particularly if the spinning elements are not balanced. A generator (or even a motor) can be built that has no such texture of its rotating parts (in fact, I have built one like that myself, as an amateur, not an engineering project). I don't believe the orientation of the motor or the generator was mentioned in your description. That would also make a difference (whether the magnus force or the air flow past the windings was in direct opposition to gravity or not).

    I doubt any of this has a bearing on your center of mass problem, but it certainly could. Does a flying aircraft or a golf ball with top spin shift the center of mass of the entire atmosphere? Depends.

    None of this is proposed as a solution. I have already given up.
     
    Last edited: Dec 18, 2016
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  19. danshawen Valued Senior Member

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    A good one to rediscover. No one including my college physics instructors worked out that the twin paradox works as well for circular paths as it does for linear ones, and as a direct result of that, an observer seated at the center of relativistic rotation actually perceives the period of rotation (time needed to complete a single cycle) as quite different from an observer traveling with an orbiting particle at the rim. At orbital velocities at or perhaps even exceeding c for counterrotating orbital paths, this is a huge difference. And it is completely practical to apply these relative time dilation effects at the rims of galactic sized spinning masses as opposed to those observed from the centers.

    Forget about "contraction" of the circumference as it is emphasized in the original formulation of the Ehrenfest paradox. It is of no relative import at all compared to time dilation, or understanding the nature of time itself. In fact, the whole idea of mixing solid geometry with time dilation is ludicrous. Pi (at rest, for a given radius) doesn't actually change. Neither does c. But T does.

    From the rim of a relative rotation, and without knowing for certain where the center of rotation actually is, it may not even be practical to ever find its location. Local relative motions are more likely to confound and dominate any effort to ascertain relative motions several parsecs distant. Time dilation is responsible for this as well. Rotations about different axes or hubs of galaxies complicate temporal dynamics even more.

    So, how large is that motor, exactly?
     
    Last edited: Dec 18, 2016
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  20. danshawen Valued Senior Member

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    Energy density. Of course. You are a genius, Q-reeus. It doesn't even matter whether the thing spinning has physical thickness or not, which is kind of cool. Changes the center of mass very nicely. Very isolated. With enough energy / mass pumped into a thin enough disk, you could collapse planets, in two dimensions anyway. The faster it spins, the more rigid the disk gets. Works with only time and energy transfer too.

    Don't need a generator in the problem at all though, do you really? Perpetual motion ideas never do much other than to confuse, but one of my favorite teachers also did this, and with the identical problem. Mr. McCool was his actual name, and he taught industrial arts / electronics. I saw my first dynomotor.

    Man, that took me a lot longer than 24 hours though. Did I ever mention, I'm just not all that bright?
     
    Last edited: Dec 19, 2016
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  21. OceanBreeze Registered Member

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    Wait. Is this supposed to be the answer to the OP? Energy density? That's it?

    Dynamotors are collapsing planets?

    Can you please elaborate a bit, you lost me.

    I am still going around in circles, I think Heaviside may have a solution for this, but he really didn't know what he was doing, and neither do I. But Damnit, it can't be that hard!
     
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  22. danshawen Valued Senior Member

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    Think of a wench motor attached to a large enough pulley system. Is there any limit to how large a center of mass it can actually move? A simple enough machine. Archimedes suggested a lever. Same thing.

    Few pause to consider, energy / mass can be transferred simply by spinning something up. As much as you want. With so many protons, if you wish. Enough to fuse tons of graphite its energy is dumped to, like in the LHC.
     
  23. Q-reeus Valued Senior Member

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    My sentiments exactly - and that's taking into account Dan's #139. You will come to find this kind of situation to be 'normal'.

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    It's not, but it does require a complete shift in perspective from what everyone (bar me) has tried so far.
     
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