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Collision with a sword placed in the wall at high speeds

  1. Sep 5, 2014 #1
    Suppose that I am wearing some super boots that can allow me to travel anywhere from 0 to about 99% of c.Now I use these boots to travel alongside a wall and this wall at some point has a very sharp sword jutting out of it. It is safe to presume that anyone with the sword in his hand can easily cut my leg in two with it (i.e. it is that sharp). So on making contact with the sword what is likely to happen? At low speeds I am likely to just cut a little skin and get out of the trajectory and roll around (i.e if only one knee is exposed to the sword) or I'll stop if both my knees are exposed to the surface of the sword. However after my velocity reaches a certain upper bound i may cut my leg in two. But what happens at even higher speeds? After a certain velocity my momentum will be enough to drive the sword out of the wall so what will happen to me in the process? Will I cut my knee in the procedure or merely cut a little skin or maybe nothing will happen to me at all?
     
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  3. Sep 5, 2014 #2

    Drakkith

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    At higher speeds, even if the sword is knocked out of the wall it will still cut through you before it is dislodged.
     
  4. Sep 5, 2014 #3

    A.T.

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    At high enough speed it will not only cut you, but eventually kill you through a shock wave propagating from the impact though your body:
    http://en.wikipedia.org/wiki/Hydrostatic_shock

    And when you really get to 99% c, then the energy becomes so high that you, the sword and the wall will disintegrate.
     
  5. Sep 5, 2014 #4

    phinds

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    And you will too

    EDIT: OOPS ... you DID cover that.
     
  6. Sep 5, 2014 #5
    But couldn't the impulse generated by me be so strong that the sword is dislodged before it cuts through me?
    p.s. I forgot to add in the original post that I'm assuming I can survive travelling at a velocity of 99% of c, of course the skin of such a being would probably be too tough to even lose a few cells by the sharpest sword ever built, but hey, it's an imaginary sword!
     
  7. Sep 5, 2014 #6
    This comic is relevant
    https://what-if.xkcd.com/1/

    At high enough energies, you should stop thinking of your body as a solid object, but rather as a collection of high energy particles which all happen to be moving in the same direction. When these high energy particles hit the sword, you have particles colliding with sword particles and changing direction. The particles behind these particles will start hitting these particles and so on, and everything explodes.
     
  8. Sep 5, 2014 #7

    A.T.

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    Why would you need thick skin? Do you mean moving at 99%c through the atmosphere? That would disintegrate you before you even hit the sword. I though you do it in vacuum.

    Well, if it's an imaginary sword and imaginary super tough skin, then you can assume some arbitrary imaginary results.
     
  9. Sep 5, 2014 #8

    BobG

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    Actually, if you wanted to dislodge the sword from the wall, you'd have to take care not to go too fast.

    The information of the collision between you and the sword can only travel at the speed of sound through the sword to where it's imbedded in the wall. If you're moving too fast, the collision is over before the sword ever has a chance to start leaving the wall.

    Fast enough and both the sword and you shatter at the point of impact (the information hasn't had time to pass to neighboring particles of the sword or neighboring particles of you), with pieces of you and sword passing right on through each other - kind of a ghosting effect.

    The end result would be your leg cut in two (with a small region shattered into tiny particles) and the sword broken in two (with a region between shattered into tiny particles).
     
  10. Sep 5, 2014 #9
    Well, I expected something similar to happen at relativistic speeds, but what if I don't have to go that fast to dislodge the sword from the wall?
    p.s. Maybe I can record the results before I die from the hydro-static shock
     
  11. Sep 5, 2014 #10
    Well, I was thinking more like the boots would squash part of my leg between my foot and knee at that speed, hence the super toughness!
     
  12. Sep 5, 2014 #11

    A.T.

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    No idea what you mean. But as I said, if you assume whatever, then you can also conclude whatever from that.
     
  13. Sep 5, 2014 #12
    So am I right in thinking that if I traveled really close to the wall and several times slower than the speed of sound and still had enough momentum to dislodge the sword, I could save my leg?
     
  14. Sep 5, 2014 #13
    What I meant was that my clothes and my boots would exert enough force on me to deform my skin. That is if I ever wanted to get to relativistic speeds in a not too long time
     
  15. Sep 5, 2014 #14

    Drakkith

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    Nope. There is no speed that you could travel where the sword would be dislodged but your legs would stay intact.
     
  16. Sep 5, 2014 #15

    phinds

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    I am reminded of the story about the man who told his doctor that every time he banged his head against a wall he got a headache. The doc advised him not to bang his head against walls.

    My advice ... stay away from the sword.
     
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