Physijs - a physics plugin for threejs. Examples Physics plugin for three.js Physijs brings a very easy to use interface to the three.js framework.
One of the reasons three.js is so popular is because it is so incredibly easy for graphics newbies to get into 3D programming. Physijs takes that philosophy to heart and makes physics simulations just as easy to run. Mrdoob/three.js - GitHub. Js examples.