1. A computer implemented method of simulating a stack of objects represented as data within memory of a computer system, said method comprising: modeling said stack within a computer simulation as a set of associated primitives with associated constraints thereto in said memory, wherein said stack comprises a plurality of layers and wherein each layer comprises at least one primitive; estimating a height for each of a plurality of primitives in said stack; determining a respective scaling factor for each of said plurality of primitives in parallel, wherein each scaling factor is operable to adjust a mass value of each of said plurality of primitives; scaling a mass value of each of said plurality of primitives in accordance with a respective scaling factor in parallel; and solving over a plurality of constraints iteratively using a scaled mass value for each of said plurality of primitives.