Arc Mastery

The Natural Path Principle

Almost all natural movement follows curved paths. Arms swing in arcs. Heads turn on arcs. Thrown objects travel parabolic arcs. When animation moves in straight lines, it immediately feels mechanical and artificial. Arcs are the signature of organic motion.

Core Theory

Anatomical basis: Bodies are systems of hinges and pivots. When a joint rotates, everything attached to it moves in an arc centered on that joint. Straight lines require mechanical rails—biology doesn't have those.

Physics basis: Gravity creates parabolic curves on projectiles. Momentum creates curved paths when direction changes. Straight-line direction changes require infinite force.

Arc Types

Circular arcs: Pure rotation around a single pivot (pendulum, door swing) Parabolic arcs: Projectile motion under gravity (jumps, throws) S-curves: Complex motion through multiple pivots (whip crack, spine movement) Figure-8 patterns: Continuous flowing motion (hips during walk, flowing cloth)