1. A method performed by one or more computer systems configured for simulating objects, the method comprising: receiving, at the one or more computer systems, a reference shape associated with an object, wherein motions and positions of the object are determined by computer simulations of the object according to the reference shape and any influences external to the object considered by the computer simulations; receiving, at the one or more computer systems, information specifying a predetermined orientation; determining, with one or more processors associated with the one or more computer systems, that the object satisfies the predetermined orientation when a portion of the object is substantially aligned with the predetermined orientation; modifying, with the one or more processors associated with the one or more computer systems, a first set of forces determined to be acting on the object by a computer simulation according to the reference shape and any influences external to the object considered by the computer simulation while the object satisfies the predetermined orientation by relaxing at least one force in the first set of forces determined to be acting on the portion of the object by the computer simulation when the portion of the object is substantially aligned with the predetermined orientation; and generating, with the one or more processors, information specifying a first position for the object resulting from the modified first set of forces, the first position being different from a second position resulting from the first set of forces determined to be acting on the object by the computer simulation according to the reference shape and any influences external to the object considered by the computer simulation.