Simulation

Physics Engine

A physics engine is software that numerically integrates the equations of motion for simulated bodies, resolving rigid-body dynamics, contact, friction, and increasingly soft-body and fluid effects. Engines widely used in robotics include MuJoCo, Bullet, NVIDIA PhysX, and Drake, which differ in contact models, solver accuracy, speed, and differentiability. Contact modeling fidelity is the key trade-off, since hard contact is mathematically stiff and expensive to resolve exactly.

Why it matters for physical AI

Every simulation-trained policy inherits the biases of its physics engine, and discrepancies in contact and friction modeling are a principal cause of sim-to-real failure in manipulation and locomotion.