Tuesday, October 27, 2009

Stop-Motion Animation

I give you a tale of lost love and reanimated corpses...

Wednesday, October 14, 2009

The Laws of Physics in an Animation Universe.

Physics in the Universe of “Shoot ‘Em Up”

Shoot ‘Em Up is an over-the-top action movie released in 2007. The opening scene shows the protagonist of the movie eating a carrot and waiting for a bus when he sees a pregnant woman fleeing from a gangster, and has no ethical choice but to intervene. The first line spoken in the movie is “You’re dead, bitch!” A few moments later, he shoves the carrot into the mouth of the bad guy, and punches it through his head, impaling his neck with it. Within two minutes, the filmmakers have told us this movie will be half “Looney Tunes” and half “Pulp Fiction”, combining surreal stunts and action with graphic violence and language. The physics of these stunts are highly distorted to heighten the action and drama in this exaggerated, living cartoon world.

There are a great number of silly action sequences in this movie. I say silly because they are so completely and utterly improbable. The filmmakers are clearly having fun with the suspension of disbelief of the audience. No one would think what they are seeing on the screen is achievable by a human being. The perception, reflexes, and accuracy of the unnamed protagonist are above super-human. They are completely instant and perfect. He can hit any target from any distance with any gun, no matter if he is carrying a baby in one hand, or carrying a woman while engaged in coitus.

There is a sequence in the film where the protagonist leaves a baby on a playground, but the antagonist shows up and tries to shoot the baby from afar. The baby is left on a metal platform with handrails that rotates around a central pivot point. When the good guy sees the bad guy take aim, the good guy shoots the handrail to make the platform spin around. The moving target makes it difficult for the bad guy to aim, buying good guy some time. He runs toward the platform to rescue the baby, continuing to shoot the handrails, making the device spin faster. Upon reaching the spinning device, he quickly snatches the baby and makes his escape.

There are a number of reasons that this would be unachievable. Getting the platform to spin would take a sustained force of leverage, taking into consideration the great mass of the device. Bullets hitting the device would hit with conderable impact, but would bounce off. In reality, if a person were to throw rocks (or shoot bullets) at a wheeled cart or wagon, it may nudge forward from the impact, but quickly come to rest. Energy is transferred by the momentum of the projectile colliding with a stationary object. However, the impact happens very quickly, and the stationary object has a large mass and a large force of inertia keeping it at rest. Six perfectly aimed 9mm rounds would not be enough to set the device in sustained motion. The force could move the platform slightly, or deform the handrails, but leverage would be required to overcome the large inertia of the device. The good guy would have to stand next to it and push.

Once the platform does begin to rotate, it will be under a centrifugal force outward away from the center of rotation. Since the baby is placed on the platform, it spins at the same velocity as the platform, and would experience the same outward force. The device is shown to spin very quickly, but the baby stays at rest near the outside of the disc, where the force would be the greatest. The platform is shown to be about ten feet in diameter, with the baby about three feet from the center. In 1.3 seconds, the platform spins 120° after just one bullet impact. That would extrapolate to 5 seconds per rotation with the baby’s path of action at a circumference of about 19 feet. The baby is therefore moving at 3.8 feet per second. I am unable to calculate the g-forces exerted on the baby, but it just plain looks wrong. The device is essentially a centrifuge. The disc rotates around and inertia pushes outward. The baby is placed on the centrifuge, and would fly off as its rotation accelerates. In the movie, however, it stays on the platform as a moving target for the bad guy, thereby creating tension while the good guy rushes to save it. When he does grab the baby from in between the handrails, he snatches it impossibly fast. In the film, the prop they used to stand in for the baby actually hits the handrail, and its stocking cap flies off of its smashed rubber head.

Another example of implausible action is a head-on car crash where the protagonist leaps from his driver seat into the opposing vehicle (a large van), and lands in the back, then quickly kills the occupants. This is analogous to a long jump in athletics. Instead of a running start, the good guy accelerates inside a car. The launch follows the law of inertia at first, but discards it in mid-air. He acrobatically dives through the windshield areas of both vehicles, travels about twenty feet horizontally and falls about five feet onto his elbows and knees, then turns around and takes out the bad guys. Long-jumpers travel comparable distances, but land in a pit of sand. Traveling that distance requires considerable force, and all of the momentum needs to decelerate the energy out. They follow inertia because they have the person launch out of a suddenly stopped moving car. Meaning the person still has all of the speed of the car, plus any push-off from jumping. Then all of that speed and momentum softly lands on the floor, gently enough for good guy to spin around. In reality, he would crumple up like a dog running into a glass door. Before the jump, while driving, he shoots out the windshields on both cars. However, automobile glass is shatter-resistant by way of laminated surfaces, and would not give way so easily. It would remain rigid and in the frame.

As for the leap itself, the acrobatics are virtually impossible. The timing of the jump and aiming of the body would be extremely difficult. The good guy would have to be crouched down in the seat, ready to spring out. Instead he is shown in the normal driving position. The good guy is then shown grabbing the dashboard as he leaves the car, perhaps helping him aim his flight. In mid-air, he is straight out, like superman. He then narrowly flies in the front window of the van, between the seats, and lands in the back area. Both cars stop and stay in place when they collide. In reality, a high-force car crash would be more messy and random than this. The cars would flip or spin or tilt up in response to the large momentum they had built up.

The movie has many fantastical conventions of the action genre. Bad guys have the accuracy of storm troopers, meaning they miss virtually every shot. When someone is shot, they jump back or flail wildly from the force of the bullet. The good guy is seen running at full speed while firing automatic weapons in each hand.

Newton’s 3rd law of motion can be stated as “for every action, there is an equal and opposite reaction” This would mean that when a gun fires, the energy of a projectile bullet is equal to the forces that propel it. The force of a bullet must have a counter energy that is manifested as recoil on the gun and its operator, plus the expanding gasses that are dispersed. If someone is shot with a bullet and the force knocks him or her back two feet, then the person firing the gun should also be knocked back two feet in the opposite direction. We know the operator is not thrown back with great force, so when someone gets knocked back by a bullet, it is Hollywood magic. Also, the force of recoil is significant and should approximate the force of the projectiles. Shooting an automatic gun, especially one handed, would be wildly inaccurate. At one pointing the movie, good guy is rappelling down a rope in the center atrium of some flights of stairs. He is holding a baby with one arm and a machine pistol in the other. He sweeps his arm around, shooting at all the bad guys climbing the stairs around him, and sends twelve of them into acrobatic fits of death.

One shootout sequence of the movie takes place in free-fall. Several characters jump out of a plane and shoot at each other in the sky. The force of air resistance would be immense in that environment. This force would act on the bullets, so they would be blown upward from the frame of reference of a falling person. Any accuracy would be exceedingly difficult, especially when our good guy isn’t wearing any goggles. Also, characters dive and climb unrealistically, maneuvering about in the air at will. Good guy dives at a bad guy, spins him around, and uses him as a human shield. At the end of this scene, all of the bodies and wreckage have fallen within a very small area, when it would be scattered over great distances.

While all of the stunts in the movie contain a grain of reality, they are highly improbable to the point of being impossible. One should take note that the name of this movie is Shoot ‘Em Up, and they didn’t bother to give any of the main characters names. Seven minutes into the movie, the protagonist says “F--- you, you f---ing f---ers.” All of these things should tell the audience to leave the real world outside of the movie theater. This movie was only concerned with making outrageous and creative action sequences, and there are many moments where I was shocked at what was going on. In its mission to be wild and entertaining, with only a wink at realism, it has succeeded. A.O. Scott of the New York Times called the film "a worthless piece of garbage.", but Roger Ebert rated it 3 ½ out of 4 stars, saying "I may disapprove of a movie for going too far, and yet have a sneaky regard for a movie that goes much, much farther than merely too far." I fall somewhere in between. I think it was just entertaining enough, and enough of a spectacle to stand on its own.