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Reactionless drive

  1. Jul 3, 2013 #1
    Is this possible?

    Inertial propulsion.

    If we take that nothing is faster than speed of light than we can take that reaction of force through matter can not be faster than c.

    If one body act on other body by force, than other body react with same amount of force to the first body.


    Lets take that in our system second body rotate certain speed around its axis.
    Example will be housing with rotating disc. Magnets will provide force. Every full circle magnets will push disc up according to housing.


    Disc rotate, so force on axis will not be in same direction as forces applied in first position


    At this point we don`t have forces witch are in 180 degree opposite direction.
    We have force that push down and second one that push housing up through axis in certain angle. Because of angle we have resultant force Fr applied.


    For example

    disc rotation speed 1 000 000 rpm, which is 104 666,66 rad/s
    r=10 m

    we have time t1 when magnet act with force on rim of disc
    we have second time t2 which is 3,34 e-8 s when force acts on axis of disc
    difference between t1 and t2 is 0,003495 rad which is 0,2 degree

    housing push against the disc in t1 and reaction to the axis happened at t2 time and act on housing in 0,2 degree
    Last edited: Jul 3, 2013
  2. jcsd
  3. Jul 3, 2013 #2

    Doc Al

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    Staff: Mentor

    Your links are incomplete. Please correct them.
  4. Jul 3, 2013 #3


    Staff: Mentor

    Without functioning links it is not possible to tell, however a device with spinning magnets will generate EM waves and those EM waves will contain a small amount of momentum. That small amount of momentum can, in principle, propel the device. It is not reactionless, it uses the momentum of EM waves.

    Of course, such a device will be horribly inefficient, like using a rocket with no nozzle and just hoping that a little more exhaust goes one way rather than the other. You will be much better off simply shining a laser off the back.

    Other than the very small amount of EM momentum there will be no net force on the device. Specifically, the internal stresses and strains that you seem to think will provide propulsion will not. Any propulsion will be purely due to asymmetric radiation of EM waves.
    Last edited: Jul 3, 2013
  5. Jul 3, 2013 #4


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    Last edited by a moderator: May 6, 2017
  6. Jul 3, 2013 #5


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    Oh I see now. You are suggesting a force applied at the circumference takes time to propagate to the axle and in that time the disc has rotated.
  7. Jul 4, 2013 #6
    Yes, that is idea. I see there is no practical usage, just wondering if this theory is correct.
  8. Jul 4, 2013 #7


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    Well no it can't be correct because the laws of physics say you can't build a reactionless drive. It's one of those situations where it's not obvious (at least to me) where the problem is but there will be one somewhere. The question is really is it worth spending time on it?

    My thinking is that you haven't considered all the forces involved in the initial "collision" between the magnets. For example it's not obvious to me that the initial forces are radial.
  9. Jul 4, 2013 #8


    Staff: Mentor

    The stresses and strains which propagate at the speed of sound do not cause any net force on the system at any time.
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