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Electromagnetic Rail gun and a circular track

  1. Sep 22, 2014 #1
    Two parallel electromagnets situated symmetrically on either side of the straight section of an oval track propel a wheeled trolley along the track, so that the trolley is in continuous motion, as long as the current is supplied to the electromagnets.

    Is this workable? Does the entry and exit speeds of the trolley have any effect on the continuity of motion of the trolley?
     
  2. jcsd
  3. Sep 22, 2014 #2

    A.T.

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    Yes. A as long you supply electrical power, it will move. It's just a different type linear motor.
     
  4. Sep 22, 2014 #3
    Does this article and diagram correctly describe the operation of this device?

    http://www.21stcentech.com/headlines-u-s-navy-test-electromagnetic-railgun/

    The reason for using an electromagnetic rail gun is that much higher projectile can be obtained than by using permanent magnets, for example if the electromagnetic railgun can accelerate a projectile from 0 upto 6,000 kmh as opposed to the 0- 40 kmh or so we see on Discovery Channel for example, or those common experiments on You Tube using permanent magnets.
     
  5. Sep 22, 2014 #4

    Nugatory

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    No. That article describes what a colleague of mine (who built one in his garage - that's a different story and less exciting than it sounds) calls a "real" rail gun. You will notice that although it is powered by electromagnetic forces, it doesn't use electromagnets as you're describing.

    (The currents and voltages involved are also extremely dangerous)
     
  6. Sep 23, 2014 #5
    I am intrigued - can you tell me where I can get information on how this railgun really works?
     
  7. Sep 23, 2014 #6

    A.T.

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  8. Sep 23, 2014 #7
  9. Sep 23, 2014 #8

    Borek

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    Good enough for starters.
     
  10. Sep 23, 2014 #9
    OK, so the thread started out by saying:

    Two parallel electromagnets situated symmetrically on either side of the straight section of an oval track propel a wheeled trolley along the track, so that the trolley is in continuous motion, as long as the current is supplied to the electromagnets.

    This works

    Imagine the electromagnets accelerate the trolley from 2 m/s to 5 ms/ sec and the trolley ends up constantly moving through on the track.

    Now if you replace the word "electromagnets" by "permanent magnets" even though the permanent magnets have the exact same accelerating effect
    2 m/s to 5 ms/ sec, the system will not work.

    Two parallel permanent magnets situated symmetrically on either side of the straight section of an oval track propel a wheeled trolley along the track, so that the trolley is in continuous motion.... no current needs to be supplied to the permanent magnets.

    I am not sure I understand how a device will stop working when its motive force is replaced by an exact equivalent motive force, however since when permanent magnets are used the system is considered to be in perpetual motion, so there is no point discussing this.

    Note that no discussion has been made as to the strength of the permanent magnets, that is, if they are strong enough to propel the trolley for 0.99 of a circuit ( not perpetual motion ) or half a circuit or more than half.

    I leave it to all who read this to think, experiment and make up their minds for themselves.

    I do not intend to discuss anything that suggests perpetual motion as this seems to be not the forum to do so.

    Thanks to all ( including admin/moderators)
     
  11. Sep 23, 2014 #10

    Borek

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    You are right about the system with electromagnets and the system with permanent magnets being equivalent (assuming these are magnets of exactly the same strength), you are just missing how it works in general.

    "Current is supplied to electromagnets" means just that - electromagnet being equivalent to the permanent magnet.

    Note that there is a difference between "continuous motion" and "continuous acceleration".

    Trick is, energy conservation doesn't allow such system to produce energy - so we don't have to analyze every possible setup in hope one of them will work differently, as energy conservation tells us - they all don't work.

    If you tell me "67894637892647890 is a prime number" I don't have to waste time factorizing it to know you are wrong - it has zero at the end, so it is divisible by 2 and 5. It is the same with any system made of magnets that can be proposed - it won't produce energy, so there is no need to waste time checking where is the error in someones reasoning, if it reasoning gives conclusion that the energy is produced.
     
  12. Sep 23, 2014 #11

    A.T.

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    What works is an "electromagnetic railgun" (as stated in the title and described in the Wiki link) that propels something within on a circular track.

    It's not an exact equivalent. Permanent magnets create a static magnetic field. The magnetic field created by the railgun rails is not static, it changes with the motion of the projectile:

    320px-Railgun-1.svg.png
     
  13. Sep 23, 2014 #12

    Borek

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    To clarify - while the magnetic field in railguns are not static, you can use electromagnets to generate a static magnetic field. There is no contradiction between different statements in this thread, as they don't refer to identical setups/situations.
     
  14. Sep 23, 2014 #13

    A.T.

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    To clarify further - When the electromagnets generate a static magnetic field, they cannot propel anything continuously on a circular track, just like permanent magnets cannot. The original post didn't specify what kind of magnetic field the electromagnets generate, and the title implied it's dynamic like in a rail-gun.
     
  15. Sep 24, 2014 #14
    The analysis of this problem is not only to do with magnetism but also with the way physics problems are analyzed on this forum. Regardless as to what works or not, and whether it would imply perpetual motion or not, like some of the other queries that I have raised, once the reason is known, we can all gain some satisfaction that we have enlarged our knowledge store.

    So to clarify even further, let's reduce this to a 'black box' problem:

    By the way, the oft - requested video on You Tube on the permanent magnet rail gun is at this location: www.youtube.com/watch?v=Vo2-Qb3fUYs

    Two steel balls each on separate identical tracks roll into a two covered tunnels running over each respective track one containing an electromagnetic rail gun and the other an arrangement of permanent magnets as shown in the rail gun experiment on you tube.

    1) Can we tell by observing the entry and exit speed of the steel ball, whether the device within the tunnel contained an electromagnetic rail gun or a permanent magnet rail gun?

    2)If no, is there anything in either arrangement that will make it impossible for the steel ball to roll in at a particular speed and roll out at a higher speed?

    3) Is it possible that in both tracks the balls roll in at 0.2 m/s and roll out at 1 m/s, depending on the strengths of the device in the tunnel assume each device can be adjusted before hand to give this result?
     
  16. Sep 24, 2014 #15

    A.T.

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    What exactly do you mean by "electromagnetic rail gun". What is described on the Railgun-Wiki and picture above? Or just some electromagnets generating static magnetic fields?
     
  17. Sep 24, 2014 #16
    Whatever arrangement works to accelerate a steel ball down a track. If the Railgun-Wiki works then that is fine.
     
  18. Sep 24, 2014 #17

    Borek

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    As far as I understand you can't reproduce railgun described in wiki with static magnets.
     
  19. Sep 24, 2014 #18

    A.T.

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    Ok, lets go with that and call it EMRG, while the other is PMRG.

    1) Yes, the speeds will decay over several loops in the PMRG case, until it will get stuck. And of course you can tell the difference by the cables providing electrical power in the EMRG case.

    2) Yes, if begin & end of the tunnel are arbitrary, you can find a section where the object speed increases, if it manages to reach the begin.

    3) Yes, you can match the speed up for the first loop. But in the PMRG case the second loop will not have the same speed at begin.
     
  20. Sep 24, 2014 #19

    Bandersnatch

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    Here's a video of a permanent magnet arrangement reflecting the linear one from the video posted earlier by aeroseek:


    As can be seen, when the initial impulse decays below what is sufficient to overcome the retarding influence of the next magnetic arrangement, the projectile stops.
    As the projectile stops, an oscilating motion can be observed, indicating that the magnets are not explicitly propelling the projectile forward, but attract it to a specific point on the track, accelerating the projectile before it gets there, and decelerating it as it passes the point.

    If you build an electromagnetic coil gun*http://en.wikipedia.org/wiki/Coilgun) to accelerate the projectile, you can turn the coils off before they start retarding the projectile. You can't turn the permanent magnets off.
     
  21. Sep 24, 2014 #20

    A.T.

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    Yes. For the arrangement in the video there could be several such points (local potential minima).

    Similarly in EM-railgun, the current and thus magnetic field disappear, when the projectile leaves the rails.
     
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