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Thread: Spooky Rotations

  1. Top | #11
    Contributor skepticalbip's Avatar
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    Quote Originally Posted by Treedbear View Post
    ... snip ...


    It would be neat to have a laser at the central axis so the beam flips directions. I wonder if this could be similar to what occurs with pulsars.
    My understanding of the current model for pulsars is that the highly directional beam of radiation is emitted from both the north and south poles of a rapidly spinning neutron star. A precession of the axis makes the beams sweep in circles. We see a 'pulse' when the direction of that circling beam sweeps past us.

    But then I or that model could be wrong.

  2. Top | #12
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    Quote Originally Posted by Treedbear View Post
    Quote Originally Posted by beero1000 View Post
    Quote Originally Posted by Gun Nut View Post
    The videos I saw showed objects "flipping" at very regular intervals. Yet those intervals are indeterminate? Or just too complicated to predict? What, then, keeps them regular?
    They are not indeterminate or unpredictable. As long as you know the moments of inertia and the initial rotational velocities you can predict the flipping period by solving Euler's equations.
    Maybe you'd know then. Does the flip need to completely occur during a single rotation?

    ETA -
    Another thing. While the angular momentum of the entire structure remains the same, it looks like the angular momentum of each individual particle of the structure reverses during the flip. It seems that during the flip the total angular momentum around the principle axis of rotation is shifted by 90 degrees and then another 90. But at the midpoint it equals zero.

    It would be neat to have a laser at the central axis so the beam flips directions. I wonder if this could be similar to what occurs with pulsars.
    This thesis has a full analytic solution worked out. There's an interesting graph of the angular momentum components on page 24.


  3. Top | #13
    Veteran Member Treedbear's Avatar
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    Quote Originally Posted by beero1000 View Post
    ...
    This thesis has a full analytic solution worked out. There's an interesting graph of the angular momentum components on page 24.

    Fascinating. Thank you very much.

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    Quote Originally Posted by beero1000 View Post
    Quote Originally Posted by Gun Nut View Post
    The videos I saw showed objects "flipping" at very regular intervals. Yet those intervals are indeterminate? Or just too complicated to predict? What, then, keeps them regular?
    They are not indeterminate or unpredictable. As long as you know the moments of inertia and the initial rotational velocities you can predict the flipping period by solving Euler's equations.
    Would that be any "easier" than, say, using physics equations to predict the outcome of a throw of dice? Is this a "technically not random - but it's really pretty darn random" thing?

  5. Top | #15
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    Quote Originally Posted by Treedbear View Post

    I wonder if this could be similar to what occurs with pulsars.
    Or Earth (!!!!!)

    That video was good... Earth is already rotating along a stable axis, they say.

  6. Top | #16
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    Quote Originally Posted by Gun Nut View Post
    Quote Originally Posted by beero1000 View Post
    Quote Originally Posted by Gun Nut View Post
    The videos I saw showed objects "flipping" at very regular intervals. Yet those intervals are indeterminate? Or just too complicated to predict? What, then, keeps them regular?
    They are not indeterminate or unpredictable. As long as you know the moments of inertia and the initial rotational velocities you can predict the flipping period by solving Euler's equations.
    Would that be any "easier" than, say, using physics equations to predict the outcome of a throw of dice? Is this a "technically not random - but it's really pretty darn random" thing?
    I would say it would be much easier than predicting the number of a roll of dice and maybe a bit harder than predicting the trajectory of a thrown ball. There definitely is a chaotic component to the unstable equilibrium, so the longer you let it go the less predictable it would be.

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