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- We actually do a lot of simulation at Pixar. Things like fire, water, and explosions are handled by the effects department. You can learn more about that in the effects lesson. The simulation department, who I work with, handles any motion attached to the characters at Pixar, like clothing and hair. But we can't move every hair on a Pixar character's head by hand, that would drive our animators crazy. Instead, we use Physics and Computer Programming. In this lesson, you'll learn how to simulate hair the same way we did for Merida in the movie "Brave". Here is an example of a shot of Merida that the simulation department got from the animation department on the film "Brave". The animators have created the main action in the scene and now it's our job to fill in the missing details such as the motion of cloth and hair. Everything we do begins with modeling the problem we want to solve. In this case, we need a physical model of Merida's curly hair. So let's begin with the very basics. What should our model of hair look like? Well, hair is kind of like a mop, just a bunch of strings. But strings are actually quite complex to model mathematically because they are so bendy. Modeling them requires a lot of computational power due to all the calculations involved. This is why we are always looking for ways to simplify our models. For example, we could take a bunch of paper clips to model a strand of hair. We first draw a series of line segments connected to particles, like this. The computer needs to calculate the positions of these particles. But first we need to describe what forces are acting on them. In the real world, each particle is affected by three forces. The force of gravity, and the forces from neighboring connections, like this. Next step, I have an interactive program for you to see this in action. You can adjust the following parameters: size of each segment, number of segments per hair, number of hairs, and the force of gravity. Explore these parameters to see what kinds of looks you can come up with. Have fun.