No force, unless a powerfully generated external force, can deviate its path to such an extent that it makes an ‘S’ around an object.
Half an hour into the movie Wanted, we see James McAvoy desperately trying to hit a target obstructed by a slaughtered pig suspended in mid-air by bending a bullet around it, but failing miserably, hitting the pound of flesh every time. That is, of course, until Angelina Jolie steps in. She stands between the target, and swirl!, the bullet bends around her and hits the concentric circles on the wall behind!
I and probably everyone else, after witnessing something so outrageous, were probably thinking the exact same thing: Who the heck would want to waste so much bacon?!
The second question, obviously, would be whether bending a bullet around an obstacle is physically possible…
The Physics behind a bending bullet
Newton’s first law of motion states that a body in motion or at rest tends to remain in motion or at rest unless or until acted upon by an external force. Basically, an object will only deviate from its course or plunge into one if acted upon by another force. So, to curl a bullet around a given point, the bullet would require an external force to change its current linear course to a non linear one. To be more precise, a centripetal force.
A centripetal force is one that binds an object in a circular motion by pulling it towards its center throughout the full motion. An object doesn’t necessarily have to make a circle; it can form momentary arcs or “almost” circles by turning in different directions.
There are only two forces that impede a bullet’s movement: Earth’s gravity and air resistance. The immense kinetic energy of a bullet is eventually dissipated by air molecules as it pierces them at such a monumental velocity and the bullet will eventually nose dive to the surface of the ground due to gravity. That being said, can gravity manifest as the centripetal force to pull the bullet in a curve?
Well… No. A bullet travels at a speed of around 1000 m/s, so the bullet’s low mass and high energy (as it exits the gun) would negate any attempt from gravity to lure it in any direction.
No matter how sharp of a turn that a fast-moving train or any vehicle makes, jumping from one of its doors wouldn’t make you swirl around the same turn. As soon as you jump, there is no force pulling you towards the center of the arc that would make you turn. You’d travel exactly along the tangent to the point of departure on the arc. Some experts believe that this would be a tad bit dangerous, particularly if attempted while driving the vehicle itself, but even if you do, make sure you close the door on your way out. More about tangential velocity motion can be read here.
As a result of what we know, the bullet will only travel straight in the direction of the tangent to the point where you shoot it, even if you’re idiotically twisting your wrists. So, yes, although your love interest standing valiantly in front of you will luckily survive, you’ll still probably end up killing someone else (hopefully not another pig).
The Role of Magnus Effect
There is another way by which a bullet could possibly be turned — the Magnus effect. This is the consequence of a spinning object in motion exerting a net force on the surrounding air, which according to Newton’s 3rd law exerts an equal and opposite force back on the moving and spinning object, thereby altering its trajectory.
This is the effect that comes into play when a football player curls the ball around a 4-man wall or a baseball pitcher throws a breaking ball pitch.
The Magnus effect requires the moving object to spin, which a bullet actually does! Bullets do not simply bust out of guns, but are forced to move through a barrel that is oddly shaped, giving the bullet a slight spin. Apparently, the spin has been proven to improve the range and performance of firearms. This is known as rifling. A more articulate article about rifling can be found here.
The Magnus effect arises because of the combinatorial play between a spinning object and the current of fluid in which it spins. The current (such as air) is then dragged along in the direction of motion, swirling the spinning object in a non-linear trajectory (upward in the above-illustrated case). Due to this effect, a baseball rotating on its vertical axis experiences a horizontal force, deviating from the otherwise expected linear path to a non-linear path.
However, again, due to its low mass and huge kinetic energy, bullets don’t allow the Magnus effect to work its magic. The bullet cannot deviate its path to such an extent that it makes an ‘S’ curve around an object. In fact, the bullet would be moving so swiftly that the effect is negligible. It is so negligible, in fact, that the strongest force amongst all those acting on the bullet is still gravity! In other words, the answer is still NO… mostly.
Note: While it’s true that the Magnus effect won’t manifest in a pistol round or any short-distance round, a long-distance round will be affected by this effect. They call it “spin drift” or gyroscoptc drift and at a 1000 yards, it averages around 8-9″ in the direction of the twist (as there are left and right hand rifling twists)
The only thing turning in that film were the physicists… in their graves. In fact, I’m sure that every science enthusiast smacked his or her head in agony after watching the tomfoolery that is the movie Wanted. I mean, if bullet bending wasn’t enough, thanks to an excess of adrenaline, the guy could also slow down his senses of time and action to pluck the wings off a housefly… with a bullet!
So, amongst all the countless deaths in the movie, the only one that bothered me was the death of Science – and the pigs, of course. Even so, no one will deny that all of it looked SO cool!