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 film 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 seeing something so monstrous, probably thought the same thing: who the heck would want to waste so much bacon!
The second question, of course, is whether it is physically possible to bend a ball around an obstacle…
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 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 nonlinear one. To be more precise, a centripetal force.
A centripetal force binds an object in a circular motion by pulling it in the direction of its center during the entire motion. An object does not necessarily have to form a circle; it can form instantaneous arcs or “almost” circles by rotating in different directions.
There are only two forces that impede the movement of a sphere: the gravity of the earth and air resistance. Air molecules eventually dissipate the immense kinetic energy of a bullet 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?
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 a curve a fast-moving train or other vehicle makes, jumping from one of its doors would not cause you to turn the same curve. Once you jump, no force pulls you toward the center of the arc that would force you to turn. You would drive right along the tangent to the starting point of the arc.
Some experts believe that this would be a bit dangerous, especially if you try it while driving the vehicle itself, but even if you do, make sure you close the door on the way out. Read more about tangential velocity 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 the Magnus effect
There is another way in which a sphere could be rotated – the Magnus effect. This is the consequence of a rotating object in motion exerting a net force on the surrounding air, which, according to Newton’s Third Law, exerts an equal and opposite force on the moving and rotating object, thereby changing 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 an oddly shaped barrel, 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 results from the combinatorial play between a spinning object and the flow of the liquid in which it rotates.
Current-like air is then dragged along in the direction of motion and whirls the spinning object upwards in a non-linear trajectory in the case shown above. As a result of this effect, a baseball that rotates around its vertical axis experiences a horizontal force that deviates from the otherwise expected linear path to a non-linear path.
However, 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 is true that the Magnus effect does not manifest itself in a pistol round or a short-range round, a long-range round will be affected by this effect. They call it “spindrift” or gyroscope drift.
The only thing turning in that film were the physicists… in their graves.
I’m sure every science buff would crush his head in agony after seeing the stupidity featured in the film Wanted. I mean, if ball 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!
Of all the countless deaths in the film, the only thing that bothered me was the death of science – and, of course, the pigs.
Still, no one will deny that it all looked SO cool!