A simple library for modeling spring dynamics


Rebound is a simple library that models Spring dynamics for the purpose of driving physical animations.


Rebound was originally written in Java to provide a lightweight physics system for Facebook Home and Chat Heads on Android. It’s now been adopted by several other Android applications. This JavaScript port was written to provide a quick way to demonstrate Rebound animations on the web for a conference talk. Since then the JavaScript version has been used to build some really nice interfaces. Check out for an example.


The Library provides a SpringSystem for maintaining a set of Spring objects and iterating those Springs through a physics solver loop until equilibrium is achieved. The Spring class is the basic animation driver provided by Rebound. By attaching a listener to a Spring, you can observe its motion. The observer function is notified of position changes on the spring as it solves for equilibrium. These position updates can be mapped to an animation range to drive animated property updates on your user interface elements (translation, rotation, scale, etc).

Check out the docco, tests, and examples for more details.