# B The movie wanted defies physic.

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1. Jan 21, 2017

### David Yu

In the movie wanted, the characters inside the movie can curve bullets by swinging the pistol, it is obvious it defies the law of physics. I know that a bullet cannot curve due to the law of motion, it is the same a sling (the thing that throw rocks) where the trajectory will always be a straight line, without earth's gravity.
Can someone tell me exactly why it is impossible, using motion and centripetal force.

2. Jan 21, 2017

### Ibix

What are the forces on the bullet after it's left the gun?

3. Jan 21, 2017

### David Yu

Gravity down, (some air resistance)

4. Jan 21, 2017

### Ibix

So the bullet trajectory doesn't curve because...

5. Jan 21, 2017

### David Yu

inertia, where there is no external force acting on it after it leaves the barrel.

6. Jan 21, 2017

### Ibix

Yes. Newton's First Law, in short.

The bullet slows because of air resistance and falls because of gravity, but there are no other forces. Other than "up and over" artillery fire (curve due to gravity), you can't hit anything you don't have a straight line shot at.

I suppose by flicking the barrel sideways you could make the bullet come out ever so slightly on the diagonal, but it would be easier to just point the gun at the target. There is also a subtle interaction between a spinning sphere or cylinder and the air called the Magnus Effect (which I only learned about just now myself), which affects bullet flight. It still doesn't let you shoot round corners by turning your gun barrel.

7. Jan 21, 2017

### Stephen Tashi

If the shooter can manage to send the bullet on a trajectory where the axis of the spinning bullet isn't aligned with the direction of flight, there could be curving effect. So to have an "air tight" argument against a trajectory curving sideways you'd have to consider that effect quantitatively. If the bullet begins to tumble in flight, the trajectory could get very complicated.

8. Jan 21, 2017

### David Yu

the bullet most likely will not tumble in the first 50 m at least, thanks to the rifling, the movie has shown that it begun to curve right after it has fired.

9. Jan 23, 2017