Science Fact or Cinematic Fiction? The Relationship Between Degree of Accuracy in Physics and Animation
In the world of animation, everything is created by hand. Our choice makes the world of animation. To achieve the reality of the animated world, it is important to have some knowledge in physics. The importance and use of physics are shown in many films, especially in the live action films with technology of computer graphics. Many CGI artists works for live action movies often say, “If nobody notices what we did in the movie, that means we did a great job.” The technology is getting better and better, so it is almost impossible to see if that is a live action footage or a computer generated footage when the job is done well. Since they are trying to create an image that goes with live actors and real footage, things have to be accurate even if it is created in computer, otherwise audience will feel something awkward in the movie.
However, in animated movie ( full CG movie such as Pixar or Dreamworks movie), audience will not feel too districted even if the physics is not accurate. Even though they follow the basic laws of physics, animated movies have more acceptable error in physics. In this paper, I will discuss one of the basic movements, jump, in different movies to analyze how they are different with what the real movements are supposed to be, and how they are acceptable for audience to watch the inaccuracy in physics. Especially, this paper will discuss four distinct style of animation, which is a 2D hand drawn film, a stop motion film, and 3D computer animated film with motion capture, and a hand animated 3D film.
First, I want to discuss the Wile E. Coyote's jump. The three main forces on jumping are gravity, support of the floor, and frictional force of the floor. If you look at a usual jump, they have to push the floor to take off. And the force generated by the push determines how much you can jump. In the episode, Zipping Along, Wile E does a highly unrealistic jump.
Let's take a look at how many frames he takes to take off.
Here is a captured frame of Wile E. Before he takes off.
And here is a very next frame.
Without having a push, it is impossible to execute a jump. Not only he does not have a push, he jumps pretty high too. Even if we do not see the apex, I can guess that he can go pretty high from the extreme motion blur.
Not only this jump, Wile E. Coyote breaks so many laws of physics in the cartoon. Yet, audience would not feel the motion is awkward and disturbing to watch because of the highly designed character and the tempo of the gags. The error in physics even helps the gags to be successful.
(Who would even expect him to do something physically right? )
Next example is from an animated stop motion movie , Tim Burton's The Nightmare Before Christmas (1993), directed by Henry Selick.
The example of error from this movie is not a big error, however, it is still a small error based on physics. Let's take a look at the minor jump of the main character, Jack Skellington. When shows up in the movie for the first time, he jumps in to a water fountain. So I will analyze the jump using the formula provided.
Here is a captured picture of crouch, take off, and the apex of the jump.
Crouch
take-off
Apex
I assume his height from the horse he is riding. And I assume that the push height of the jump as 1.9 feet. Also, the measured jump magnification is approximately 3.5.
Based on the formula,
Jump Magnification=(push Factor) x (Push Height in Feet)
I can get that push factor is about 1.8. If the push factor is 1.8, the push time should be about 4.5 frames. In the film, the push time is about 6 frames. (Push factor for 6frames is 1.) To be accurate in physics, this jump should either be higher or have less push time. Even though there is a minor error in physics, the movement in the movie is totally acceptable to the audience. Like the Wile E's Example, the characters are highly designed. Also, the style of stop-motion film helps the audience to not be too concerned about the accuracy of the movement itself. The example I discussed was really minor error. So it seems there is not point of discussing such a minor error. However, it is interesting since audience are disturbed by the inaccuracy of the movement in some movies with different style.
Next example is animated movie, but it has more realistic look since it is in 3D. In a movie, Polar Express (2004,) there is a scene where the conductor gives kids a refreshment of hot chocolate.
While they are dancing there is a somersault, which has error in physics. First, let's look at the three picture of crouch, take-off, and apex of the jump. I picked the man in the middle since it is the easiest one to see.
(I put red dots on Center of Gravity)
Crouch
Take-Off
Apex
From this information, I can gather several factors to judge this jump. Assuming the guy's height is about 6feet, the push height is about from his pelvis to knee. So, I would say it is 1.5 feet. Also, the jump height is roughly 3times of push height. Using the formulas provided earlier, I can collect the numbers below.
Push Height=1.5ft Jump Magnification=3 Push Factor=2(based on formula)
With the push factor of 2, the push time should be about between 4 and 5 frames in 24fps. However, in this scene, the push time is actually 3 frames. It sounds really nitpicking, but if the push time is 3 frames instead of 4.5 frames, the guy should jump about 9 feet instead of 4.5feet based on the formula of the jump multiplier. It is almost twice as high as it is in the movie. In this case, one frame gives a pretty big difference. Also, one hand holds a tea cup, so they cannot have enough hand movement to support flipping.
Though the example I talked about on Polar Express sounds a little nitpicking. The important thing is that the polar express has a lot of small error in physics like the example. Because of those small errors, we find the motion is a little awkward. In the previous examples in the other movies had bigger and exaggerated errors in physics. Yet, they are still acceptable to audience. Polar Express used a lot of motion captures with a tweak. So, the movement tends to have a feel of being a copy of real movement. And the character's design and proportion are more realistic than other films I mentioned. As I mentioned in the beginning, the more realistic they look, the more accuracy they need. Even though they try to incorporate breaking the laws of physics, we starts to find errors unacceptable as soon as the image gets too realistic.
Even though 3D movie has more realistic feel than a 2D films. It does not mean creating error in physics always makes a disturbing motion to the audience.
For example, we can look at how the character in The Incredibles (2004) jumps differently.
For example, Helen's jump incorporate stretch of her body, and the movement itself is unrealistic. Edna Mode's jump is a little choppy due to her low apex compared to her push height. And all the character has a distinct way of jumping. And most of them slightly breaks the laws of physics. However, it is a choice to add a characteristic to each character, like they enhance the gag in Wile E. Coyote's case.
As a conclusion, the error in physics are easily found in many animated movie. But the import thing to remember as a creator of movie is to determine how much accuracy do they need for their particular movie. Sometimes, creating an error in physics is disturbing, but in other cases, it is acceptable, or even good choice to have an error . In the interview for the VFX artists from the recent film, 2012 , they said there were 25 people (including mathematician, physicist, programmer, etc. )working on a 2 seconds scene for six months to create a whole collapsing town of LA in computer. They needed that much accuracy in physics since the movie was live action, and they cannot put something looks computer generated. Whereas, Wile E. Coyote always breaks so many laws of physics, yet that makes him really comical and funny. In any cases, it is important to know the real physics, because we cannot break the law properly without knowing what they are. It is just like you have to study models at figure drawing to draw cartoon characters better. Knowing the relationship between accuracy in physics and the style of the movie is a great help for any filmmakers.
Note: I changed my topic after I did the outline since the outline was talking about three different thing in three scene. So, I made it about same error in three different movie so that it follows the guideline of the paper.
