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Action and Reaction

  1. Jul 13, 2004 #1
    This is probably off the wall but I would like some other peoples opinions none the less.

    Imagine two 10kg, 1 meter long pipes that are closed off at each end. At the ends are magnet coils to propel and object back and forth. Inside the pipes there is a magnet disk/ball/whatever that is 1kg.

    Both of these pipes are situated on a platform in order to swing the pipes around like a centrifuge. Each pipe will swing the opposite way in order to cancel out any other movement.

    Both pipes are parallel to each other, with the ball in each of them, at the same end. The magnetic coils are now activated to send the ball flying to the other end at 10m/s. When the ball hits the other end the pipes are the swung around in opposite directions. Rinse and repeat.

    It seems to me such a device, in space, would create movement without expelling anything. Essentially you create a reaction which gets the pipes moving at 1m/s opposite of the ball. When the ball hits the other side the whole apparatus would stop. However it would have moved.

    Perhaps I’m crazy but please prove it wrong? :rofl:
  2. jcsd
  3. Jul 13, 2004 #2
    first point is are we too assume no frictional forces take place?
    second point is we a dealing with a closed system were no external energy sources are affecting this so all the energy would be either kinetic or potetial.
    some of this energy would be converted into heat .
  4. Jul 13, 2004 #3
    Of course there would be friction and some energy would be lost to this. It is electically powered though.

    The whole point is its a system that would propel a mass in space without a reaction. It does this by delaying the reaction by a fraction of a second. Granted you never really could get up to a high speed with such device.
  5. Jul 13, 2004 #4
    the problem is in your "rotation". The object is heavier on one end, to symetrically rotate it in space creating "no movement' you would have to rotate around the center of gravity which is offset. this will bring your device full swing back to its original location.

    was good thinking though, i approve
  6. Jul 13, 2004 #5
    Yes it is heavier in one end for 90 degrees. After that the weight would be on the other side and move it back. If you spin an object 180 degrees you will be at your starting location.
  7. Jul 13, 2004 #6
    i think you mean 360 degrees
  8. Jul 13, 2004 #7
    Yes if your talking only using one object.
    We are using two pipes here though. Each pipe at this instant would have the 1kg ball on one side. The pipes would be parallel to each other and then swung 1 clockwise and the other counterclockwise. All the centripetal forces would be canceled out when they stop.

    Its kind of hard to describe this without showing a diagram. Sorry if its vague.
  9. Jul 13, 2004 #8
    as far as equilibrium goes, rotating an offset mass in space exerts a force on the axis of rotation proportionate to the amount of the offset

    rotating your device 180 degrees with the mass offset (rotation about the center axis <.5 meter mark>) will create the force to push the device back to where it started.

    rotating the device about the center of gravity or center of mass would nullify this force being exerted, but by virtue of having a longer end of pipe on one side, you're gonna end up at square 1 anyways
  10. Jul 13, 2004 #9
    this is my analysis using my admittedly limited knowledge of physics

    we need to get some of the physics Big-heads in here for a proper appraisal, really. I am not that confident in my answers

    or we can build one and take to space

  11. Jul 13, 2004 #10
    I dont think the whole idea is properlly being conveyed. How do I post a diagram? :uhh:

    Yes, in usual systems the whole device would be back to square one. However in this idea the math says it wont :)


    Oh btw, supposable angular and linear movement are reserved to each other. One can not change angular movement to linear and visa versa. So technically rotating a mass 'shouldnt' move the system at all.
    Last edited: Jul 13, 2004
  12. Jul 13, 2004 #11
    you GOT me on that one... ::uhh::
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