[Simulacrum0]

i wish you well on rolling your own Physics. Its certainly straightfoward to implement formulas for kinematics/dynamics as you suggest, but like the first comment references, timesteps and stability are quite elusive to get manageable for varying amounts of moving objects. While stacking might be an isolated case, i could definitely see the scope expanding beyond initial estimates for 'final tuning'. Bullet does a good job w/ stacked cubes and i'd expect PhysX to be equally proficient.