Science Fact or Cinematic Fiction?

Since the advent of animated feature films, storytellers have been able to bring new and original experiences to their audience. The 2006 film “Monster House” is one of those stories that would not have been technically feasible without advanced animation techniques. Animated movies have come quite a long way since “Snow White” in 1937. Today, 3d animation is the standard, and it brings a visual richness that would be nearly impossible on painted cels. But no matter how beautiful the images are, if they aren't moving around with just the right subtleties, the audience can quickly tell, and that puts their suspension of disbelief in jeopardy. However, with fancy camera work and rapid action, filmmakers can “get away” with breaking a lot of rules in the name of suspense.

As viewers, we know that a movie is a constructed reality. We know not all movies are documentaries. We willingly ask to be transported to a realm of entertainment. Even when the audience is “going along for the ride”, animators should try to ground their work in the laws of the physical world, so that the world of the film feels believable. We recognize things on the screen from our real world, and expect them to behave a certain way. Storytellers should be very deliberate in breaking these expectations. We want enhanced reality, not phony acting. When we spot something that we don't agree with, it breaks the spell of the storytellers.

Monster House was made by Imagemovers, a motion-capture based animation studio. They were responsible for derailing The Polar Express with their stiff robotic pseudo-humans. Instead of duplicating that photo-real but emotion-dead approach, the studio wisely explored a new visual style. Monster House looks and feels more cartoony, but still has a little bit of stiffness issues. I very much enjoyed this movie, and thought they handled the visuals very well. They still strive for near-photo realism, but at least the characters are allowed to have shape and personality.

The titular house is the crown jewel of the movie. It's simply amazing to watch it both subtly shift expression and to transform completely. In the story, the house is possessed by an unruly spirit, and eats anything that may venture on it's lawn. The heroes of the film are three children who set out to unravel the mystery of the house and stop its tyranny.

The action of the movie reaches a climax during a scene where the three children are trying to destroy the house after it has grown arms and legs and chased them into a construction pit. Two of the children are up on a crane, and one is on the ground being pursued by the house. One of the kids on the crane, DJ, throws dynamite down the chimney and then swoops up the fleeing friend, whisking the both of them to safety. Jenny remains on top of the crane, and watches the explosion from above. This scene is well-manipulated by the director to excite and engage the audience, but it contains a number of physical inconsistencies.

DJ is on the underside of the boom (the horizontal extension of the crane) waiting for Jenny to light the dynamite. He is hanging on to a hook that is on a cable that hangs from the crane when in use. He engages a lever by accident and the hook is released, which swings out from the end of the crane much like a pendulum. However, a pendulum may only swing to the same height it was released at, naturally diminishing in height due to air resistance. The force that propels the pendulum is gravity, which would be stored in a resting state as potential energy. The potential energy increases with height. In the movie, the hook swings past it's starting height to reach an apex above the boom. At the apex, the hook has a higher potential energy than where it started, without any outside forces acting to push it up higher. This is cinematic fiction! The plot calls for him to swing higher so that he can call out to Jenny and she can toss him the dynamite. If this was staged below the boom, it would be more difficult for the characters to interact.

Once DJ gets the dynamite, he swings back towards the tower part of the crane, and the swing reaches its apex right at the tower, so that DJ is able to reach out and grab the tower to pause for a moment. The swing started about halfway out on the boom, but now the cable is extended to the full length of the boom. If the cable was slack when the swing started, it would first drop and jolt before oscillating in a smaller pendulum motion. If the reel of cable was free to unwind and extend out the length of cable, DJ and the hook would not come to a pause at the top of the apex. So the cable has inexplicably lengthened.

So DJ has swing up next to the tower of the crane, and reaches out to brace up against it for a moment. He gets one arm and one leg around the crossbars, and holds on to the hook with the other arm and leg. He pauses there for a moment to size up the house, then swings out to go for it. At this moment, he is holding the weight of the hook apparatus and a great deal of weight of the steel cable. The hook part is about the same size as him, but is presumably made of steel. This moment passes fairly quickly on screen, but caught my attention as being utterly improbable.

Having swung out from the tower, DJ lobs the lit dynamite into the chimney of the house, and swings away to rescue Chowder, his friend on the ground. We see DJ approach on the swinging cable, but his path of action is no longer on a plane. Now he's swinging circumferentially, as if someone has rotated the boom. Another possibility is that he pushed off against the house to change his trajectory, but he was shown swinging above the top of it. Where is the action-reaction that altered his inertia? An outside force must have acted on him in order for him to behave this way.

Altered trajectory aside, DJ is swooping down to rescue Chowder. It's a good thing that the cable has lengthened, because now DJ is close enough to the ground to reach his friend. He swings by right next to Chowder, which is good because there is nothing DJ could have done to steer the pendulum. DJ reaches out and picks up Chowder, then they quickly jump off and land in a ditch while the explosion passes over their heads.

Anyone who has transported a dead body can tell you that a human being is heavy. Picking up and carrying an entire person takes a lot of effort. Lifting the equivalent of your entire body weight requires balance and a lot of muscle coordination. To compound things, DJ is thin and Chowder is pudgy. There is no way that a skinny child could lift a fat child with one arm.

Even if DJ had the requisite strength to lift his friend, he is traveling at great speed, and would have to accelerate Chowder very quickly in order to pull him along. The situation is analogous to reaching outside of a moving vehicle and grabbing something. The resting object has inertia, and forces must be exerted on it to get it moving. No sensible human adult would reach out of their car door and try to snatch up a 150-pound weight. Your arm would snap off! Likewise with the movie scenario.

While DJ and Chowder hide from the explosion, Jennie gets barbecued directly above the massive fireball. She is seen recoiling and shielding her face from the heat, which looks dangerously close to her. As we learned in class, the space above a flame is even hotter than the center of the flame. That means Jenny is in serious trouble. Also, dynamite is a high explosive, and detonates with a significant shock wave, which would likely rattle her brain or send her off her precarious ledge. All of this would wreak havoc on a fragile human body, but Jenny is all polygons, so she survives.

Monster House is an adventure. It's a fun and engrossing film that creates its own reality, one that is a deviation from our own. It walks a fine line between realism and cartoon, and is bound to slip its toes on either side along the way. If I were not an animation student training my critical eye and analyzing the physics of what I see, I would probably not have noticed the impossible action near the end of the movie. Then again, the entire premise of the movie is that a house is possessed with a human spirit and comes to life. The whole thing depends on impossible action.