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Would this experiment work?

  1. Feb 14, 2010 #1

    First I want to say that I'm not a physicist. I'm just a layman.

    Well, I'm very disturbed with an experiment that I had imagined and I wish someone would help me understand if my reasoning would be correct...

    First of all, I wish to know if this experiment could work in a laboratory:

    http://img202.imageshack.us/img202/2290/experiment.gif [Broken]

    (I put this drawn on ImageShack to facilitate viewing of the idea).

    This is NOT my "final" experiment yet. First I need to know if this one should work.

    Explaining this first experiment:

    It would be a large electro-magnet, capable of generating a magnetic field strong enough to magnetically attract a metal disc located five meters away.
    The metal disc was placed on "support rails", but would be free to move forward and backward. The disk would be initially located 1 centimeter away from a wall of glass. When the electro-magnet was activated, would attract the metal disk, which would collide with the glass wall, which would prevent the disk's advance forward. Thus, while the electro-magnet was turned on, the metal disc would be stuck on the glass wall.

    My first question: Is this experiment possible? Would it work this way?

    If you consider this experiment is possible, I will explain my whole idea, that is an "extrapolation" of this experiment.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 14, 2010 #2
    The experiment is physically sound. Your only problems would be selecting the material of the disk, it would need to be highly ferromagnetic (strong attraction to magnetic fields) such as iron and generating a large enough magnetic field to attract something 5 meters away.
  4. Feb 14, 2010 #3
    Nice. I'm very happy to know it should work. Now, my question is:

    If we could make an eletro-magnet more strong, with a stronger magnetic field (measured in gauss), would it attract the metallic disc from a greater distance?

    Instead of just 5 meter, it would be possible to place the glass wall and the disc at a distance of 200 meters from the "giant" eletro-magnet, and the "giant" magnetic field attract the disc and make it move 1 centimeter and collide with the glass wall?

    If yes, then I will extrapolate the idea to the "final" level.
  5. Feb 14, 2010 #4
    Theoretically, yes. On engineering scale, probably not.
  6. Feb 14, 2010 #5
    Cool... So, the "final" steep:

    Imagine that NASA can make a "mega-giant" eletro-magnet and put it in the outer space...

    Imagine that the glass wall and the Disc can be put in a spaceship 900 thousand kilometers away from the "mega-giant" eletro-magnet...

    The 900 thousand kilometers distance was chosen by me because it requires 3 seconds to light to cross that distance.

    So the BIG QUESTION is:

    When NASA activate the "mega-giant" eletro-magnet, that disc 900 thousand kilometers away will move INSTANTLY?

    Or it will take 3 seconds before the disc moves that 1 centimeter and collide with the glass wall?

    (Sorry if I didn't expressed myself in an understandable way, English is not my first language).
  7. Feb 14, 2010 #6


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    Magnetic force, similar to electric force and electromagnetic wave, travels at the speed of light. Both magnetic interaction and electric interaction are described classically via Maxwell equations. So there is no such thing as "instantaneous" for such an interaction.

  8. Feb 14, 2010 #7
    Eaxctly what Zz said. It would take three seconds, at least in your frame of reference. But let us not get into that.
  9. Feb 14, 2010 #8
    Hummm.. So it's really impossible to transmit information faster than speed of light...

    Thanks a lot!
  10. Feb 14, 2010 #9
    Blimey, you opening up a can or worms there. Its impossible with what we currently know. Though if tachyons ever prove to exist then that is another matter.
  11. Feb 14, 2010 #10
    Wait a minute!

    I had another "crazy" idea!

    If it were built in the outer space a very large bar of 900 thousand kilometers in length, and there was an engine so powerful that it could push one end of the bar, making the whole bar to move some 5 centimeters forward in a single bound ...

    If I were at one end of the bar, and you were at the other end ... Then you activate the engine and makes the entire bar move some five centimeters ... 900 thousand kilometers away I see the movement at the other end of the bar!

    That would be instantaneous, no? It would not take me 3 seconds to receive the information that you activated the engine!

    In this case, the information would travel 900 thousand kilometers in less than 3 seconds! We would be transmitting information at a speed greater than that of light! Or not?
  12. Feb 14, 2010 #11


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    We get that question a lot. There is no such thing as a perfectly rigid bar and in fact, the impulse of the push will only travel through the bar at the speed of sound in the bar, which is a lot slower than the speed of light.
  13. Feb 14, 2010 #12


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    To add to what Russ has said, you need to remember that a solid is built by atoms/molecules that are held together in a rigid lattice/position via electromagnetic forces! So what I've said above still applies. You are STILL limited, at best by the speed that each of the vibrations being transferred via EM interactions.

  14. Feb 14, 2010 #13
    Hummm... I understand... So, I think I'm convinced... I will stop trying to think about a manner to astronauts in a tripulated mission to Mars could communicate instantly with Earth...
  15. Feb 14, 2010 #14
    Excellent you have highlighted a problem that would occur if special relativity did not exist.
    As Russ said there is no such thing as a perfectly rigid body due to special relativity. If you are interested in this sort of physics then read up on special relativity.
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