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Stiffness and damping

Springs connected in strands create bouncy hair simulations. To make it more realistic, we add dampers to resist fast changes and settle hair quickly. Balancing spring stiffness and damping achieves the desired artistic look. Experiment with these settings for realistic hair behavior.

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Video transcript

(metal clattering) - Now that you are comfortable with how springs expand and contract, we can try something a little bit different. Let's try connecting a bunch of springs together like this. When we simulate springs, we don't draw them using the zigzag pattern. Instead we use lines, which can expand and contract. This gives us a really bouncy strand of hair, but it's a bit too bouncy. Notice the hairs take a really long time to settle down. This isn't very realistic. Take a look at our reference shots again. See how quickly the hairs come to rest, just a few bounces. You might think changing the spring stiffness will fix this, but look what happens. Both low and high stiffness values still result in hair which never settles down. Our solution to this is adding what's called a damper to each spring. A damper is something that resists fast changes in displacement, and it's used to bring springs to rest much more quickly. Check this out. Here we have the same strand of hair as before, except each spring is connected to a damper, and we can change the amount of dampening using this new parameter. If we increase damping, the springs resist quick changes, and therefore come to rest much faster. However, too much damping will result in really stiff hair, which isn't natural, and here's what it looks like with a whole bunch of hair. We went through a similar exercise in the early stages of modeling Merida's hair. We were trying to get the right mixture of spring stiffnesses and damping so that we could achieve the desired artistic look, but with the wrong settings, the springs start fighting each other, and you get pretty funny results. So the trick is to find a nice balance between spring stiffness and damping. You can try this out in the next exercise. Here you can control damping of each spring, number of hairs, number of springs per hair, and spring stiffness. See if you can come up with something that behaves a bit more realistically.