Arcs are the natural, curved trajectories that most objects and people follow during movement, and they are essential for rendering a realistic and aesthetically appealing animation. In real life, motion rarely follows a perfectly straight line, whether it’s the arc of a character’s arm, the launch of a ball, or a head’s rotation, most motions trace curved paths because of gravity. Without them, movement can seem rigid, artificial, or unrealistic. For instance, when a character waves, their hand traces a gentle curve instead of a sharp or straight line.