Hey, I hope you have seen Disney/Pixar's "Up". It's a gorgeous movie, especially if you see it in 3D, and a fun and even emotional storyline. So don't miss it.
One of the behind-the-scene things for "Up" is the realistic simulation of many aspect of the movie. This is especially true in the scenes involving those numerous balloons. Pixar animators are well-versed in physics, and have tried to model them according to the laws of physics.
May said that the animation department at Pixar never even considered hand-animating the balloons. But even standard computer animation wouldn't be up to the task, because of the N-squared complexity involved in the thousands of interdependent balloons. Instead, the studio's computer whizzes figured out a way to turn the problem over to a programmed physical simulator, which, employing Newtonian physics, was able to address the animation problem.
"These are relatively simple physical equations, so you program them into the computer and therefore kind of let the computer animate things for you, using those physics," said May. "So in every frame of the animation, (the computer can) literally compute the forces acting on those balloons, (so) that they're buoyant, that their strings are attached, that wind is blowing through them. And based on those forces, we can compute how the balloon should move."
Still, there's one very obvious inconsistency between the physics and what is on the screen. I'm not trying to be nitpicking here, because I love the movie, and as an animation and a movie, one should allow for a lot of artistic license in telling the story. Still, when I saw the scene in the movie, the physicist in me wanted to ask the question.
The scene involves the infamous moment when Carl's house was pulled up from the ground and floated away due to all these helium-filled balloons. Forgetting that it would probably take an unbelievable amount of balloons to do such a thing, what "bothered" me was the idea that there's no buoyancy until the balloons were "deployed". Here's what I mean.
When a couple of people from a retirement home came to pick up Carl, he handed his bags to them and told them to wait for him while he said goodbye to his house. He then went in, and then deployed all the balloons that are attached to a base in his fireplace. All these balloons then started to pull on the house, breaking it off its foundation, and the house became afloat.
But see, the balloons were already in the house. All Carl did was simply to "unleash" them so that they now float freely. But it doesn't mean that before then, they do not have the buoyancy. By simply unleashing them, it doesn't mean that the upward force suddenly got turned on. It was there all along, and Carl's house should have floated away as soon has he has filled up and attached a sufficient number of balloons.
What would have been realistic would have been some anchor that Carl would had to release to finally allow the upward force to finally overcome all the remaining part of the house and become free from the foundation. Since they are paying that much attention to the physics, this would have been more accurate. But I don't believe I saw this in the movie.
Oh well, it is still a damn fine movie. Go see it!