Saturday, June 28, 2008

Wanted - The Movie

When asked: "can a bullet curve" as per the trailers in the movie Wanted

My answer was: sorta, kinda, but no. Not really.

The dynamics of it are barely plausible in theory, and pretty much impossible in real life.

However, I will take a crack at it.

First, the aerodynamics of the bullet itself (as well as the recoil of the gun) can see it rise a little, for a very, very short period, then gravity takes over, thereby demonstrating that a rather serious curve already exists in the vertical plane. Hold on to that thought for a minute.

No bullet actually comes out of the barrel perfectly straight. However, it will follow, what's known in missile parlance as, a spin-stabilized path. This means that, barring external force, the gyroscopic inertia produced by the spinning missile will force it to go in a straight line perpendicular to the rotational plane.

Now then, gravity is a constant external force – which explains the down-curved path, as seen above.

So, to imprint a curve on a spinning bullet you would need to exert a force "while" it is travelling.

In relation to a fixed point, say on the ground, the bullet curves while travelling down the barrel and while the gun is being moved. Upon exiting the barrel however, the bullet should then keep going straight on its last "affected" trajectory. Think of the rock spinning on the end of a string, when you let go the string, the rock will then travel straight along the last tangent to the circle since the external force 'holding the string' is no longer in play.

You might be able to kick the bullet's ass sideways a little as it comes out of the barrel to impinge a wobble or tumble, but not a curve per se. Also, to get such a maneuver right is beyond human means. A bullet can travel several hundred feet per second. Out of a 6 inch barrel? That's ½ a foot in which to make your move, and then a micrometer would be required to nudge the bullet as it comes out at precisely the right distance and time. Not bloody likely.

Now, the game dynamics of jai-alai or lacrosse, and even baseball, tells us that you can indeed greatly curve a ball given the right amount of movement and tool, etc. However, a lacrosse ball would actually be spinning in a parallel plane to the travel, not perpendicular to it as a bullet does. Same goes for a curveball in baseball. The reason it works is that the ball is not spinning perpendicular to the plane in which it is travelling. The gyroscopic effect being skewed away from the straight path, not inline with it.

The bottom line? A bullet only spins one way, and that spin is imprinted by the barrel's rifling (see why we call them rifles?). If you manage to impart a spin in any other direction, then in real life the bullet will tumble ass over end or it will wobble. There might be a theoretical limit whereby a bullet won't tumble, but it's pretty much impossible for it not to wobble.

Neither of these vehicles, wobble nor tumble, will ever allow a consistent "curve".

So no.

But I'm allowing for some physicist to prove me wrong.

Oh, and I haven’t seen the movie yet.


Blogger MedStudentWife said...

you and Fidel would have a lovely talk :)

obtw... some other thoughts (beyond this post)

July 05, 2008 11:59 p.m.  

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