Principle number seven in my list of animation principles is

ARCS:

For me arcs were one of the biggest ‘I get it’ moments in animation. Once I started using arcs my animation seemed to be so much more fluid and appealing.

So what are arcs?

Very simply they are the shapes that are made by following a point on the animation, or at least they should be if your goal is to create a fluid movement.

One example that’s mentioned in The animators survival kit by the great Richard Williams (Who Framed Roget Rabbit) is that of a running horse animation. His story recalls one of the animators at Disney was struggling with the animation, in particular the head movement just didn’t look right.
The other animator (I can’t recall who) placed a dot on each frame where the horse’s eye was. After he’d drawn a dot on each frame of the animation, he then drew a line through the middle of each dot. The line was jagged and wiggled all over the place. This was the problem.
He then drew an up and down wave motion, or arcs, by getting the drawings to follow the arcs, the horse's movement became natural and fluid.

In fact some animators even use  white board pens to track an objects movement using the exact same technique of placing a dot on their monitor screen at the point of the object being tracked.

There’s also plugins out there that can do it within the software, which might be a safer bet if you don’t want to run the risk of accidentally using a permanent marker and ruining your screen forever!

Organic things generally move in arcs. Think of your arm, if you lift it and traced the movement of the tip of your finger, it would form an arc. The reason being is most things move from one pivot point, although the faster an action is the narrower the arc appears. For example someone throwing a ball casually would produce quite a large arc in their arm movement. Where as a baseball player will throw as hard as he can, keeping the ball centered as much as possible.

So rule of thumb is, bigger arcs generally give a looser feel to an animation, where as straighter arcs are used when objects are moving faster.

After a while you start to notice the natural arcs that things make, which makes it a lot easier dissecting the movement, if something doesn’t look quite right.

As I mentioned at the start, learning the rule of arcs really helped improve my animation.
It’s not a magic bullet and all the other principles need to be applied but if your animation is just feeling a little messy and lacks an organic feel and fluidity then checking your arcs could just the solution. 

Hope that is of some use and again any questions or comments just give me a shout.

And if you need help with some animation then feel free to drop me a line.

Till next time,

Peter