Physical simulation has become commonplace in computer animation because it produces realistic motion automatically. The animator specifies simulation parameters such as the initial positions and velocities of objects, and the simulator computes the corresponding physical motion. The resulting motion, however, is difficult to design; even a small adjustment of the simulation parameters can drastically change the subsequent motion.

Two semi-automatic techniques are introduced for designing the physical motion of few passive rigid bodies: without any self-propelling forces or linkages and with simple mathematical models of frictionless collision. Interaction is an integral component of the new approaches. The interactive editing technique allows the animator to design the entire physical motion by dragging a body, at any point in time, to a desired position. The sketching technique allows the animator to design the physical motion of bodies by acting out their motion with hand gestures. Both design tools transform a description of how bodies should move into a physical motion that matches the description as closely as possible.

86 pages

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