Arc is a reflection of the underlying force, converting its strength into velocity and curvature. A successful arc allows viewers to feel this hidden sense of energy.

On surface, arc seems rather simple to understand and easily put into animated applications; but if without regards to its invisible side, path of arc might appear hollow and mechanical, lacking organic senses.

In common-sense physics, soft forces allow higher degree of curvature, creating lyrical and more complex series of unfolding arcs; stronger forces cause arc to be straighter and simpler, lesser in degrees of flexibility.

Since in animation, we can plot any arc paths and structures will follow; we can defy reality, but they have to feel ‘right’ and comfortable to look at in motion.

In short, strength of internal force (embodied in character’s structure and make of mass), interacting with gravity and other external forces determine the curvature, distance and path of arc.

(In example above, the rough animation follows a higher degree of curvature, generating a more relax feeling; but in the final animation, it followed a straighter curve, giving a more hurried and streamline look. This was an implemented design choice from a production I’ve worked on, helping to define a certain sense of light-hearted and mischievousness to character.)