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Why did the bullets curve in the Wanted movie? Why did they not follow Newton's law of Motion?

Was there an in-universe explanation given for why they would act in such a counter intuitive way? Or is there a real world explanation for how it would be accomplished?

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    Two words: Artistic License – gnovice Jul 3 '12 at 16:53
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    That's like asking why most aliens have two legs and two arms, or why Arnold Schwarzenegger still stands at the end of the movie against all odds or why Xena wears a body armor which has zero protective value. – Bobby Jul 3 '12 at 17:29
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    I would say that while wanted doesn't actually follow Newton's laws it does make an attempt to pretend they are. The bullets curving are explained by a combination of super human reaction speed and the altered bullet itself. While we know for a fact (shown to us by Mythbusters) this won't actually curve a bullet, it's a better explanation than: "Artistic License". – onewho Jul 3 '12 at 17:40
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    @Bobby I wouldn't say zero protective value. Perhaps only 5-10%, but that's still something! =^_^= – Izkata Jul 3 '12 at 20:20
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    @Bobby - It makes it hard for the enemy to concentrate on his/her shooting, especially if she's in motion... Isn't that kind of standard for all female armor in fantasy? The less material, the greater the armor class advantage via distraction.. See the TVTropes entry – K-H-W Jul 3 '12 at 21:14
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Yes, Wanted doesn't follow Newton's Laws of Motion.

However, the movie itself does attempt to explain how bullets are curved through the air.

Each of the assassins have the superhuman ability to speed up their heart to a super-accelerated rate; this enables them to move at a super fast speed and exert superhuman force. When this speed and force is focused on flinging and firing a gun the bullet is curved through the air.

Also most of the bullets they use aren't perfect, they have engravings which (within the context of the movie) alters its flight pattern.

But again, these movie physics aren't based in reality. Mythbusters proved that even with super human speed and force, along with an altered bullet, a bullet could not be curved as shown in the movie.

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    Mythbusters video: youtube.com/watch?v=EFMQSdJXyF4 – Force Flow Sep 13 '12 at 22:13
  • Hah! With some artistic license and a half-explanation, maybe the curving bullet doesn't make my head explode. That a bread truck could keep up with a sports car, however... – Thom Brannan Mar 5 '13 at 11:30
  • Note that there are guided bullets prototyped at Sandia that change trajectory to track a laser target. And that there are smart munitions that explode after N distance is flown. – Patrick Hughes May 25 '14 at 16:29
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The logic was that they were using the marks on the bullet plus that motion of the gun while firing to result in a curving effect, the same way (but more dramatically) as you would curve a baseball. (The carving on the bullet acting the same way as the stitching on the baseball, amplifying the effect of the spin on the air pressure.)

Realistic? No. But allowing for superhuman skill and some artistic license, at least entertaining enough to allow suspension of disbelief.

  • You can see why the writers might think the example of a curveball makes this plausible, but a little more knowledge of physics shows this doesn't make sense. Changing the path of a moving object means changing the momentum vector, done by applying a force for some time, since change in momentum is force integrated over time. With a curveball this force is due to different air pressures on each side, created by its spin and stitching; but a bullet has a much larger momentum than a ball, and there's much less time for the air to apply a force to it, so the change to its direction would be tiny. – Hypnosifl May 25 '14 at 17:01
  • Link on the physics of curveballs, if anyone's curious: ffden-2.phys.uaf.edu/211_fall2002.web.dir/jon_drobnis/… – Hypnosifl May 25 '14 at 17:02
  • Actually, I may have failed to take into account that because the bullet is moving faster, the force the air exerts on it is much greater, which could balance out the smaller time the force is exerted; Patrick Hughes mentioned the guided bullets from Sandia above, and I found an article at share.sandia.gov/news/resources/news_releases/bullet/… which says it controls the trajectory by adjusting tiny fins on the side, so it is air that's providing the force to change its path. The video at youtube.com/watch?v=KLwVVYV3_K4 suggests the change in angle is small tho. – Hypnosifl May 25 '14 at 17:40
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I'm going to assume we qualitatively follow Newton's Laws, even if we don't crunch numbers to prove so.

Just so we're on the same page, here are Newton's laws or Motion:

  • First law: If an object experiences no net force, then its velocity is constant: the object is either at rest (if its velocity is zero), or it moves in a straight line with constant speed (if its velocity is nonzero).
  • Second law: The acceleration a of a body is parallel and directly proportional to the net force F acting on the body, is in the direction of the net force, and is inversely proportional to the mass m of the body, i.e., F = ma.
  • Third law: When a first body exerts a force F1 on a second body, the second body simultaneously exerts a force F2 = −F1 on the first body. This means that F1 and F2 are equal in magnitude and opposite in direction.

So from the first law we see that we need a constant acceleration towards the centre of rotation (Swinging the arm when firing only affects the starting velocity, not the acceleration), this requires a force to act on the bullet originating from the same direction, and this would then push against the originator of the force.

So we have two options, as I see it: A force external to the system acts on the bullet, or the forces already acting on the bullet, i.e. air resistance.

Bullet Diagram

So we can see the velocity the bullet would go before the extra force was applied, the new 'curved' velocity and the force required...

An external force would have to be some electromagnetic force, but I can't imagine that being exerted by an assassin, who would need powers like Magneto.

I've wracked my brains for about 10 minutes thinking of a way to get a force towards a point so we have a curved trajectory, and the solution is the lame looking spoilers/wings on the back of the bullet, and no rifling. It's the only solution (I could think of) that would cause the trajectory we see in the film.

But really, it's not possible. The spoilers would be unreliable at best I'd imagine. A ball could be fired in such a way that the spin could cause it to curve, but making it spin in the barrel would be another challenge, for another day.

  • One other possibility would be to have the bullet itself expel some highly pressurized gas in a sideways direction, pushing it in the opposite direction like a rocket, but I don't think this is consistent with how the bullets were depicted in Wanted. – Hypnosifl May 25 '14 at 17:32

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