In this lesson we're gonna learn about the principle  of arcs and how once you begin to observe the natural world,  that most motion comes in some form of an arc. It's very rare that something can move in an  exactly a straight line. So if you take a look at some of these examples, you can see  that the arcs come in all shapes  and sizes, big, small, asymmetrical,  but that everything has some kind of an arc to it. And one main reason for that is  because of joints, how they move. And because a joint rotates,  that means the limbs are gonna move in an arc shape. So once you begin to look for this, you'll begin  to see arcs everywhere.

Back in the day when Disney began to embrace this principle,  their animations became much more fluid and natural looking. Before their animations of their characters were very rigid  and they would walk straight up  and down, kind of like a piston in an engine. And once they began to embrace arcs,  their characters hips would bounce  and roll over from step to step in an arc fashion instead  of a straight up and down motion. This principle is valuable both at the planning stage  of animation and at the Polish stage of animation. So you could encounter this at the beginning  and at the end of the process of animating something. It's a great way to plot out your animation  to make sure the path of motion has no rough edges to it.

And path of motion is a term you might hear,  and that's not to be confused with line of action,  which is something  that you might hear when you're doing gesture  or figure drawing, where one  of the first strokes you make when you're doing that is, uh,  the line of action to get the kind of through line of  how the character is positioned and posed. What we're talking about is the path of motion,  how something moves through a scene over time. So here I am in the iPad app procreate,  where you can create a path with your brush  and set it as a background layer so  that each new frame you make,  you can be sure you're on the right arc and path of motion. And that's an example of planning your animation using arcs. And toward the end of an animation, especially in 3D, I love  to use it to polish my animation  to make sure the arcs are moving smoothly. And I learned this, you know, the importance  of it from a visitor we had  to our school when I was learning animation  was Lino de Salvo.

He was the head of animation for Frozen,  and then he was the animation supervisor untangled. And when he came to visit our school  and talked to us as students, he impressed upon us  how when he was animating on in those films  that he made sure at the end of doing his animation,  he would go through each single joint of the character  and make sure that each arc  of those joints was moving exactly how he wanted them to. And they were a nice fluid arc. And that's one of the reasons why those Disney animations  look so nice and appealing. So in my own animations,  one way I will make sure the arcs are working  is I'll pick the extreme part  of a body, part of a character. If I'm doing character animation.

So for example, one commonplace I'll  pick is the tip of the nose. So I'll track the motion of the tip of the nose  because even though I'm using the head joint to rotate,  I want to pick something that's further away from that joint  that I'm actually animating and track its arc. So I'll pick something as far away from that joint as I can,  and then I'll track the motion of that arc around. And then I'll also maybe pick the top of the head  and I'll track these two arcs around to make sure  that they're doing exactly what I want them to be doing and  or if I'm maybe not even sure what I want them to be doing. At a bare minimum, I don't want  to see any hitches in those paths of motion. I want them to be nice fluid arcs.

So in my student film here, you can see that I  had a character with a stick  and I, at an early stage of learning animation, I realized  how important arcs were. Because of this animation, I had to track not just the arc  of the wrist of the character moving the stick, I also had  to track the tip of the stick. So I was tracking two arcs at once  and I needed to make sure that they were somewhat related  to each other, so  that way it looked like the character actually had control  over the stick and not the other way around. So that the tip of the stick was kind  of following the motion of the wrist  and that they were working in tandem together. Because the arm can move like this, but if I'm holding a pen  or a pencil, I could also do this. So if I'm only tracking this, I'm not tracking any  of the motion at actually the tip of the stick.

So I was tracking this motion of where this was  and what the wrist was doing. These were happening all at the same time. So that's why I had to make sure I was tracking both  of those points of animation and that they were nice fluid  and that the shape of those  were an arcs, some kind of an arc. And typically when I'm going through an animation  and I've, I've made my first pass or even second  or third pass at the animation and I,  and something doesn't feel right, it's almost always  because the arcs aren't working. And so I'll have to kind of go into detective mode  and start checking each joint or control  and try to find out where the arcs aren't working. And nine times outta 10, if it comes  to something I can't really put my  finger on why it's not working.

It almost always comes down to an art somewhere is not  as fluid as it could be. And the path of it has maybe a bit of a hitch in it. Instead of being a nice curve,  there could maybe be a little point  where it jets out and then keeps going. So that's maybe more for 3D animation  because you're depending on, um, some of the key frames  to interpolate between,  and the computer doesn't know what you want to do if, if  that happens and you're not putting  a key frame on every frame. So that's maybe a bit more for 3D animation,  but just goes to show how important arcs are  and how I use it every single day  and every animation I've ever done. But it's good to keep in mind.

You know, one of the big challenges I had early on  was understanding the style of animation I was in. So early in my career I was doing more cartoony animation. I was making animated shorts for the mobile  game Clash of Clans. And so that was much more cartoony  and the arcs needed to be really fluid and nice. And when I made the transition into working into visual  effects, meaning photoreal animation with CG characters,  I brought that same appeal in wanting  to have the arcs be nice and smooth as they could be. And some of the notes I actually got back from the animation  supervisor was, the arcs are too smooth,  which is something I'd never heard before  because I had only ever been animating in this kind of nice,  uh, cartoony style  and I'd never had to work with something  a bit more organic, like real photo,  make something look photoreal.

And so it's good to know what the goal is  and the kind of style you're working in  because that could dictate whether  or not you might need to actually add a little bit  of noise into the arc  and instead of it being super fluid throughout. So that was a lesson I learned early on in my career  that has helped me make the distinction  between cartoony animation  and something that's more photoreal and make the switch back  and forth and know deliberately those choices I'm making  to make sure either I'm making the rcx very smooth  or maybe I'm adding a little bit of noise in there  to account for jostling and more, you know, organic  and photo real things that happen in real life. Conversely, if we compare that with 2D animation drawing,  that the difference could be, it's, it's very easy  to create linear interpolations between drawings  or in-betweens. And we're gonna see that more in this assignment. Uh, we're gonna do after this lesson as an example. So let's just review what we've learned about  arcs in this lecture.

So we've learned that arcs are part of the natural world  and that's why there's a lot of innate appeal. And just by the virtue of how things move in nature,  that makes our eye attuned to  that appealing quality of arcs. Then we learned how arcs are important at the beginning  of animation, the planning stage,  and at the end during polish,  and how that can be different between the style  of animation you're using. And we're gonna get into more 2D examples here in this  assignment coming up. So stay tuned for that. And we are gonna create a nice head turn animation over the  next few assignments.

We're gonna keep working on this animation. We're gonna learn another two principles  and continue to work on this assignment  through those principles. 'cause we're gonna keep applying what we're learning  onto the same assignment as we progress and learn more. So thanks for watching now, we'll see you in  that assignment lesson.