These remind me of particle collisions. A set of particles go in, and a set of particles go out, with momentum and angular momentum conserved. But instead of ab

These remind me of particle collisions. A set of particles go in, and a set of particles go out, with momentum and angular momentum conserved. But instead of abstract mathematical "points", the particles in this case are smooth and free of singularities. Also, their interactions occur at a distance in a way that makes intuitive sense.