Arcing bullets

edited October 2008 in Movies and Shows
Has anybody seen the movie Wanted? It's a recent movie with James McAvoy, Angelina Jolie, and Morgan Freeman. McAvoy is an average dude who gets recruited into being a professional assassin in some fraternity. I dunno, I missed the beginning of the movie, but that's the gist of it.

In the movie, the members of the fraternity are all expert shots, and they have the ability to arc their shots. They do this by apparently swinging their arms with a lot of force. This way the assassins can shoot something that is obstructed by something in front of them, or they can shoot without a direct line of sight.

I was talking with my friends while watching this, and one of my friends was wondering why it isn't possible. I haven't taken physics in about eight years or so, so I'm pretty fuzzy in this area. My friend thought that it was indeed impossible to arc them to the degree that they did in the movie, but they thought it might be possible to give them at least a very slight arc in trajectory.

I said that swinging the gun in an arc before shooting it wouldn't make a difference, because the bullet already has to travel straight through the barrel anyway, so the barrel sets the trajectory, not the motion of the gun beforehand.

But I didn't do a good job of explaining it, and I'm not entirely sure if I'm right on this. I abandoned studies of the sciences many years ago, so I'm pretty rusty. Anyone out there know what I'm talking about, and can you explain it? You will seem even more credible if you can prove it mathematically.

Comments

  • edited October 2008
    It seems to me that you're probably right. Maybe we should think about how you would throw an arcing baseball. It's not about swinging your arm to the left or right while you throw, it's about giving the ball a certain type of spin when you release it, right? So swinging the barrel to the side shouldn't do shit.

    Besides... that sounds like a stupid concept anyway. Reminds me of Jumper for some reason..... ugh.
  • edited October 2008
    Newton's second law states that once an object is in motion it will continue along its path until another force acts on it, so basically once it leaves the gun, that fucker's going straight until it hits something or gravity has its way with it.
  • edited October 2008
    Ha, funny this question was asked... my ex's brother-in-law is a math genius, and a bunch of us asked him how it would be possible for Angelina Jolie to curve a bullet all the way around the room. Apparently he sent back a very detailed e-mail on how it would be possible, and other details that were interesting...

    He said that yes, it IS possible to curve a bullet, but you would have to apply an insane amount of force on the gun right as the gun was shooting-- way more force than any man (or Angelina Jolie) would be able to produce.

    He also figured out that in order for a bullet to be curved around a room, it would first have to be curved like he had explained, and then there would have to be a little black hole directly in the center of the room.

    I don't know how possible it would be for me to get the e-mail forwarded to me, but I'll ask. He's a funny guy, the math genius; he once figured out, after being asked by my ex's sister, how big would a water balloon have to be to put out the sun. Funny stuff!
  • edited October 2008
    If you were swinging your arm in an arc, the bullet would come out of whatever angle the gun is, (straight out of the barrel) and the only motion the bullet would take is downward, due to gravity. As Night Lord pointed out, newton states "once an object is in motion it will continue along its path until another force acts upon it" the only way it could spiral like it does, or even arc, would be if gravity reversed itself on the bullet for a short period of time.

    It would be easier to show if i could scan a drawing or something
  • edited October 2008
    It's pretty much as people have described, when a bullet is fired, only one force is being applied to it. Spinning your arm wouldn't apply a large enough force to affect anything other than making your shot wildly inaccurate.
  • edited October 2008
    Is it good or bad that this is making me think about how I'd make a mod in Unreal Tournament that would allow you to arc a shot by flailing the gun as you shoot?

    Except that if I was gonna mod things again I've got plenty of more fun/interesting/useful ideas.

    Edit: Well, not a mod so much as a new gun.
  • edited October 2008
    I never saw the movie just because of the arcing bullets in the commercial. I think I have a different idea of the arc, too. When you have a ball, you can put a spin on it and throw it out at and angle and it will follow an outwardly spiraling path (see diagram A), such that if there were no gravity or other forces impeding the ball, it would make a full revolution. OR you can simple apply a sideways force on the ball in addition to the forward force, cause the path to shift. But it will still be a straight path (see diagram B).
    balls.jpg
    But as a bullet is an elongated object exiting from a barrel with roughly the same interior diameter as the diameter of the bullet, you can't put this kind of a horizontal, rotational force without actually spinning the bullet by just knocking the one end of it at the moment it exits the barrel of the gun. (see diagram C)
    bullet.jpg

    But to do this, you'd actually have to be moving your arm in the opposite direction of the arc. Or you could create that same force by swinging in teh direction of the arc and stopping really fast with perfect timing so the bullet is teetered over the edge of the barrel.
  • edited October 2008
    Adam wins. That was fucking awesome.

    Okay, when I was trying to explain swinging your arms, I was trying to describe picture B, I think. It would have a slanted trajectory, but it would still be going in a straight line. But then in theory if somene used spherical bullets and a specially manufactured a gun that put spin on them, then it could be possible, right? I'm not talking about wild arcs in the movie, just a little bit of an arc.
  • edited October 2008
    Serephel wrote: »
    Adam wins. That was fucking awesome.

    Okay, when I was trying to explain swinging your arms, I was trying to describe picture B, I think. It would have a slanted trajectory, but it would still be going in a straight line. But then in theory if somene used spherical bullets and a specially manufactured a gun that put spin on them, then it could be possible, right? I'm not talking about wild arcs in the movie, just a little bit of an arc.

    The barrel would probably have to be curved though, like in a spiral. The bullets might not fire properly, massacring the velocity of the projectile, or simply destroying the gun. Not saying it's not possible, just not probable.
  • edited October 2008
    When I imagined a gun to put spin on them I imagined a pistol with a barrel a bit longer than that of a pea shooter with the explosion chamber (the chamber where the explosion the shoots out the projectile takes place) slightly to one side or the other. Maybe it could be adjustable for curve in either direction.
  • edited October 2008
    You'd also probably need special bullets. Baseballs curve when spun because the stitches in them help catch the air. A spherical bullet my arc the slightest bit over a long trajectory but it would be easier to prove the concept if there were little air-catching notches or something in the bullet. Course this would all make it totally inaccurate.

    I don't think that would work either nolonger, the barrel would still be confining the bullet so that only one force affects it. To make a bullet curve, a force would have to be applied after or as it's leaving the barrel of the gun.
  • edited October 2008
    I know it wouldn't work, that's just what I thought.
  • edited October 2008
    If it has spin, something will affect it affter it leaves the barrel, The air.

    :tmyk:
  • edited October 2008
    If it has spin, something will affect it affter it leaves the barrel, The air.

    :tmyk:

    :objection:

    Yes, but the air isn't technically a force, it only affected the bullet's velocity, it doesn't force it in any direction.
  • edited October 2008
    Stunning rebuttal! You make Phoenix Wright proud.
  • edited October 2008
    See the Magnus effect.

    So it is possible in a sense. But the problem is the round would need to be spherical, and even then its cross sectional area is tiny and air is not dense enough of a fluid. And of course it could only slightly curve over a very long distance, not even close to as short as the length of a room.

    So Panda is correct in that the air is not a force, but it does create forces.
  • edited October 2008
    Stunning rebuttal! You make Phoenix Wright proud.

    Why thank you!

    EDIT: Read Fuzzy's article.
    So I guess technically the air is a force, but only because the bullet makes it so?