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Not all motion is added by the animators, some motion, including the fish in Giulia’s hand and water falling from the fountain are simulated effects.

Computer programs create automated motion

What is simulation?

While animators focus on acting, simulation programmers create motion that makes scenes feel alive and believable. Some simulations –– hair, fur, and clothing–– respond to the way a character moves. Other simulations recreate natural phenomena, such as fire or water.

What does a simulation technical director do?

Simulation technical directors use computer programs to create effects and to move hair and clothing. Programmers start with a physics-based simulator, but then they fine tune it to balance believability with the artistic needs as well as the time it takes to compute the simulation.

The left half of this frame from Brave includes the simulated elements (hair and clothing) that are missing from the right half of the frame.

The left half of this frame from Brave includes the simulated elements (hair and clothing) that are missing from the right half of the frame.

Videos and Activities

Pixar’s Simulation Challenge

Creating curly hair with physics

Pixar’s Simulation Challenge

David Ryu

Global Technical Director

David Ryu

Crowd Simulation Workstation

Simulate the motion of a school of fish

Adjust sliders to change the rules governing the motion of fish for Finding Nemo. Vary the distance between fish, the number of groups, and the desire to match the direction of other fish and see the effects on an animated scene.


Pixar in a Box

Continue to explore using Pixar in a Box, a set of lessons developed by Pixar and Khan Academy. Follow the links for lessons on Simulation and Effects.

Ask a Pixar Scientist

  • Is the animation of the computer generated grass determined by the actual observation of real grass, or is there some imagination mixed in?
    — Kevin
    It will start with observation of real grass, but it will be simplified so the computer can handle it. It is also likely to be idealised to make the grass fit in with the look of the film, which is cartoon-style rather than photo-realistic, so will involve some imagination.
    — Peter Collingridge; Khan Academy
  • Do you like to draw or just like to create art in the computer?
    — Lillian
    Thanks for the question! I like to do both, and pretty often I find that I get the best answer when I use both to get there. I can use a pencil to draw what I want to do, use math to see how to get there efficiently, and put the art and math together in the computer to create the image. I also use drawing as a communication tool with other departments.

    Drawing with a pencil helps one practice looking at and understanding form and composition, even if the computer is one's preferred tool for creating images. If you're interested in computer graphics, I recommend you practice making images with both. Best of luck and keep learning!
    — Fran Kalal; Lead Technical Director, Pixar