Barbell space craft thought experiment question

Discussion in 'Physics & Math' started by keith1, Sep 20, 2010.

  1. keith1 Guest

    A barbell-shaped space craft is constructed of two perfectly round and equal size sphere compartments, of the same weight, joined by a tubular corridor or connecting passageway. Both spheres contain equal amounts/weights of cargo and crew.

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    Both spheres are accelerated to a certain speed, so that the tubular corridor is perpendicular or 90 degrees to the direction of travel and both spheres are traveling at matched speed.
    Using the following equation as a guide:

    p=mv
    (momentum = mass x velocity)

    Give your best guess as to what would occur if all the crew moved themselves, and all the cargo, into one sphere, leaving the other empty:

    a). No change observed. Both spheres are connected, so the adjustment in mass placement is without effect.

    b). The empty sphere begins to lag behind the full sphere.

    c). The full sphere begins to lag behind the empty sphere.

    d). The space craft starts spinning on its axis.

    e). The space craft starts rotating along its length.

    f). Not enough data to give a clear answer. I haven't a clue.

    g). Other. Explain.
     
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  3. cluelusshusbund + Public Dilemma + Valued Senior Member

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    g). No change woud be observed whether the spheres was conected or not.!!!
     
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  5. James R Just this guy, you know? Staff Member

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    Answer: g.

    All that would happen after everybody stopped moving around would be that the two spheres and connecting tunnel will have moved sideways a little (perpendicular to the direction of travel). This occurs since the centre of mass of the entire arrangement has shifted. The two spheres will still be travelling level with each other, without one lagging behind the other. The overall speed of the craft through space will not have changed, and it will not have started to rotate in any way.
     
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  7. keith1 Guest

    Now the craft speed is increased to .8C speed:

    The relativistic momentum is given by

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    which is the ordinary definition of momentum with the mass replaced by the relativistic mass:

    The increase in effective mass with speed is given by the expression

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    courtesy: /hyperphysics.phy-astr.gsu.edu

    Again extrapolate as to above, to what would occur if all the crew moved themselves, and all the cargo, into one sphere, leaving the other empty:

    1) James R's answer "g" above would remain a viable observation from some observation point.

    2) The two spheres share the same juxtaposed location, from some observation point.

    3). both 1) and 2) are viable observations.

    4). neither observation is viable at these speeds.

    5). Not enough data to give a clear answer. I haven't a clue.

    6). Other. Explain.
     
  8. AlexG Like nailing Jello to a tree Valued Senior Member

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    Is the ship still being accelerated? Or is it an inertial frame.

    And if being accelerated, is the motive force lined up through the center of gravity, or does it act on the ship as a whole?
     
  9. keith1 Guest

    The ship is an inertial frame. But please include alternate thoughts, in both states.

    I suppose the center of gravity is initially at the midpoint of the connecting corridor, until the mass is transferred...?
     
  10. AlexG Like nailing Jello to a tree Valued Senior Member

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    If the ship is in an inertial frame, it shouldn't matter where the center of gravity is. If there's no force acting upon the ship, and no angular momentum to contend with, the path and orientation of the ship will be unchanged.
     
  11. John99 Banned Banned

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    22,046
    So you have two engines at opposing end instead of one engine located in the center. Either way ther would need to be compensation. Although, ideally, something like that travelling through space would be better operated like a sail boat whereas it can operate with no mechanical power but that is true for anything. In this case a burst method would provide power. Obviously moving up,down or level would be a factor as well.

    To give some insight into op: The main components are time, weight and power.

    The weight is not just the weight og objects moved but also weight overall. The time is in relation to the limits or how close to limits the engines are working at. Instead of throttling down the engines would better be employed using the burst method but just a matter of efficiency and engineering.
     
  12. keith1 Guest

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    The last installment of this exploratory involves the same .8C speed condition arranged above, save that the tubular corridor is now parallel to the direction of travel, so that one sphere (A) is directly leading inline, ahead of the sphere (B) trailing behind.

    Again extrapolate as to what would occur if all the crew moved themselves, and all the cargo, into one sphere, leaving the other empty:

    1) by moving the cargo B forward to join the cargo A.
    2) by moving the entire total cargo from A to B (opposed to the direction of travel).
    3) by moving the entire total cargo from B to A. (advancing toward the direction of travel).
     

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