Unity’s built-in 3D physics engine is an integration of the PhysX engine in close partnership with NVIDIA. PhysX is available directly through the Editor.

NVIDIA PhysX SDK is an open source, scalable real-time physics engine that enables advanced simulations for more immersive game play with true-to-life simulations and real-time dynamic effects. PhysX is a library for representing 3D worlds that lets you create and destroy actors and tracks their explicit or proximity-based interactions.

PhysX SDK’s dynamics simulation capability includes support for collision, joints, and actuation using maximal and/or reduced coordinates. You can also query the world using a number of different tools, ranging from simple ray casts to sweep and overlap tests.