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### Course: Pixar in a Box > Unit 4

Lesson 1: Hair simulation 101# Support springs

Curly hair animation uses damped springs for realistic movement. Support springs, added between larger springs, create curls at rest. Adjusting support spring stiffness and length controls curl size and shape. This technique brings Merida's hair to life, offering a fun way to explore spring physics!

## Want to join the conversation?

- Is it like bézier curves while before it was linear interpolation?(9 votes)
- How did the team built up the function of parameters? How did they calculate the net force?(8 votes)
- how does support springs even work?(2 votes)
- The support spings make the points they connect on the hair "want to stay close".

:et's think about only one support string:

Without it, the only force on the hair is the gravity , so "it wants" to fall straight down.

With one support spring, there is a force pulling the two connected point together. So te hair wont fall straight down, but would make some arc between the 2 points.

Now, with many support springs, we have many arcs.

I beliave they used another layer of support strings connecting the first one (or even more), so all the arc continue one another in a smooth way.(5 votes)

- I don't understand this very well but what if you were able to add a compound that would keep the hair curly without needing spring support(2 votes)
- Did you know that pausing the video gives you points easily? I didn’t(2 votes)
- why is the video stuck at half waY??(2 votes)
- great work so far we build up a model of hair using a series of damped Springs this gives us a more realistic behavior like this style I came up with but remember the art department once Merida's hair to be curly sometimes it curls up while moving but it doesn't hold that curly shape while at rest here's an idea what if we put some smaller Springs in between the larger Springs to pull them together let's call them support Springs we already have a mathematical model of the spring so this is easy to test out if I connect a support spring between the larger Springs I'd get something like this if I hide the support Springs you'll notice the hair comes to rest in a curly shape that's much better adding these support Springs results in new parameters we can control the stiffness and length of the support Springs shorter support Springs will give us smaller curls while really long support Springs give us bigger ones and if we make the support Springs have a higher stiffness the curl pops up like this kind of like we applied hairspray compare this to support Springs with lower stiffness in this case the curls relax a bit and fall downwards in a natural way now let's try this with a bunch of hairs now that's starting to look more like Merida this isn't exactly the method we use on Merida for the movie but it's close in this next interactive you can try this out with all the parameters we've introduced the two new parameters are support spring stiffness and support spring length see what you can come up with(2 votes)
- great work so far we build up a model of hair using a series of damped Springs this gives us a more realistic behavior like this style I came up with but remember the art department once Merida's hair to be curly sometimes it curls up while moving but it doesn't hold that curly shape while at rest here's an idea what if we put some smaller Springs in between the larger Springs to pull them together let's call them support Springs we already have a mathematical model of the spring so this is easy to test out if I connect a support spring between the larger Springs I'd get something like this if I hide the support Springs you'll notice the hair comes to rest in a curly shape that's much better adding these support Springs results in new parameters we can control the stiffness and length of the support Springs shorter support Springs will give us smaller curls while really long support Springs give us bigger ones and if we make the support Springs have a higher stiffness the curl pops up like this kind of like we applied hairspray compare this to support Springs with lower stiffness in this case the curls relax a bit and fall downwards in a natural way now let's try this with a bunch of hairs now that's starting to look more like Merida this isn't exactly the method we use on Merida for the movie but it's close in this next interactive you can try this out with all the parameters we've introduced the two new parameters are support spring stiffness and support spring length see what you can come up with(1 vote)

- Can you make support strings in real life?(2 votes)
- so how do you create the hair?(1 vote)
- Hopefully they'll explain it the way they actually do it in the future!(2 votes)

- wowzers! These effects are pretty epic! [Cool Face Emoji](1 vote)

## Video transcript

(jumping, bouncing) (light switches on) - Great work. So far we've built up a model of hair using a series of damped springs. This gives us a more realistic behavior, like this style I came up with. But remember, the art department wants Merida's hair to be curly. Sometimes it curls up
while moving but it doesn't hold that curly shape while at rest. Here's an idea. What if we put some
smaller springs in between the larger springs to pull them together? Let's call them support springs. We already have a mathematical
model of the spring so this is easy to test out. If I connect a support
spring between the larger springs, I get something like this. If I hide the support springs,
you'll notice the hair comes to a rest in a curly shape. That's much better. Adding these support springs results in new parameters we can control. The stiffness and length
of the support springs. Shorter support springs
will give us smaller curls, while really long support
springs give us bigger ones. And if we make the support
springs have a higher stiffness the curl pops up like this. Kind of like we applied hairspray. Compare this to support
springs with lower stiffness. In this case, the curls relax a bit and fall downwards in a natural way. Now, let's try this with a bunch of hairs. Now that's starting to
look more like Merida. This isn't exactly the
method we used on Merida for the movie, but it's close. In this next interactive
you can try this out with all the parameters we've introduced. The two new parameters are
support spring stiffness and support spring length. See what you can come up with.