A physics simulation engine simulates the motion of one or more particles that represent virtual objects in a virtual graphics scene. Each particle is assigned to a level in a particle hierarchy that has at least two levels. The physics simulation engine collapses constraints associated with particles assigned to a first level of the particle hierarchy to generate hierarchical constraints associated with particles assigned to the second level of the particle hierarchy. The physics simulation engine updates the position of each particle assigned to the second level of the particle hierarchy by enforcing constraints associated with the particle. The physics simulation engine then updates the position of each particle assigned to the first level of the particle hierarchy based on the positions of the particles assigned to the second level of the particle hierarchy.