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What happens if you hit a bullet from the side?

  1. Jul 26, 2015 #1
    My brother actually said this and felt that it would not effect the person's hand. He said, theoretically, if a person were to move their hand from the side of the bullet (so as to slap the bullet) , at the same speed as the bullet, the bullet would would change its direction and the hand would be left unharmed. I feel that the bullet would graze the person's hand, while it is in contact with the bullet, also the speed of the hand does not need to be at the same speed as the bullet to cause it to change direction, it would require a certain amount but not exactly the same as the bullet.
    Which one is right and why?
    also here is a picture I made in case I could not explain the problem properly: http://imgur.com/ceATo5d
    Thank you!
     
  2. jcsd
  3. Jul 26, 2015 #2

    Bystander

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    You have a collision between two objects. Is it elastic, or inelastic?
     
  4. Jul 26, 2015 #3
    I guess this collision would be elastic since a hand is a soft object.
    Either way though there will be some exchange of momentum.
    The moving hand may very slightly alter the trajectory of the bullet,
    however the much faster moving bullet could apply a very considerable force to a part of the hand which it touches, and very possibly this could result in grazing or worse damage depending on factors such as the exact angle of contact
     
  5. Jul 26, 2015 #4
    If the hit is made at a 90o angle
     
  6. Jul 26, 2015 #5
    Probably would result in a nasty graze along with some tissue damage due to heat caused by friction, but no permanent injury.
    The trajectory of the bullet would probably be altered by a very small amount.
     
  7. Jul 26, 2015 #6

    mfb

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    That is my expectation as well. A frictionless cold bullet would not harm the hand (assuming it is completely flat to make that collision exactly as described).
     
  8. Jul 26, 2015 #7
    1889_20_280-gunshot-wound-hand.jpg
    Bullet grazing wounds to the palm and wrist.
     
  9. Jul 26, 2015 #8

    DaveC426913

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    I realize you're trying to make an ideal scenario here, to isolate the mechanisms, but I'm not sure that discounting friction illuminates the issue here. Of course a frictionless bullet would do no harm.
     
  10. Jul 26, 2015 #9
    If you were to hit the bullet and cause the exact force of the bullet it would change direction with no effect. But if the force of the object hitting it was less then the force measured with the speed of the bullet it would cause damage. Also this all depends on the angle of hitting the bullet and the direction it was hit. To the side up or down gravity does play effect in this equation
     
  11. Jul 26, 2015 #10

    DaveC426913

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    I refute both these claims.

    We're talking about a human hand here. Damage can and probably will occur regardless of whether the oblique force is equal, less than or greater than the momentum of the bullet.
     
  12. Jul 26, 2015 #11
    If your talking about heat yes but for the amount of time touching the bullet there would not be enough time to transfer the heat needed to cause damage
     
  13. Jul 26, 2015 #12
    Regardless of skin blood bone or metal if the force is exact then their shouldn't be variants
     
  14. Jul 26, 2015 #13

    Vanadium 50

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    A bullet moves at 1000 mph. People don't move that fast.
     
  15. Jul 26, 2015 #14
    His question was theoretical
     
  16. Jul 26, 2015 #15
    This won't work. You have a 1700 mph bullet and 1700 mph hand. They have a collision velocity of 1700*sqrt(2) = 2400 miles per hour. The bullet puts a hole in the hand no matter how cold or frictionless it is.
     
  17. Jul 26, 2015 #16
    I can say that I have 'experimental evidence' that a very brief contact of human flesh with a hot object (such as a soldering iron) will cause tissue damage.
     
  18. Jul 26, 2015 #17

    Bystander

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    That was my take on the OP as written. The other possible "twist" is that "The Bulletproof Monk" can parallel the trajectory for a couple milliseconds and "tap/slap/nudge" it sideways by some measureable amount.
     
  19. Jul 26, 2015 #18
    At a 90 degree angle it would knock the bullet of its course but at and degree above that I believe yes it would go through the skin probably at twice the speed of a stationary hand
     
  20. Jul 26, 2015 #19
    No. In the center of velocity frame you just get hit by a faster bullet. Bystander understands what trajectory is required of the magical 1700+ mph hand.
     
  21. Jul 26, 2015 #20
    Do you propose constructing a lab with the object of impact having the same elasticity and angle!?
     
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