Almost nothing in nature moves in straight, mechanical-like lines. The inclusion of subtle (or not so subtle) Arcs greatly increases the beauty and natural way things can move. Any movement, simple or complex, is a series of rotating and counter-rotating arcs.
But more importantly, Arcs are gestures or lines of action; they are what give your animation consistency and flow, whereas straight lines give power and emphasis.
Example the series of head movements in Remy pictured. His head doesn’t just pivot left and right – it sweeps down, over and up again. His nose is a great indicator of where is head it pointing, but of course every character in the film is moving in Arcs!
Even if your character is just statically sitting there, the animation can still be engaging and interesting to watch. Remember: if it’s boring on screen, the viewer is bored too. Animation does not simply mean Movement!
Watching your arcs isn’t limited to large limb movements. Subtle movements are just as important; the rolling motion of the hips, the rise and fall of the head in a walk, the sweep of a head turning… even the movement of your eyes.
Arcs add clarity to your action, and make a drastic difference to the quality and appeal of your animation.
From Frank Thomas and Ollie Johnson:
Arcs give animation a more natural action and better flow. Think of natural movements in the terms of a pendulum swinging. All arm movement, head turns and even eye movements are executed on an arcs.
That’s it for Remy and I on the Principles of Animation– thanks for reading! Ciao!