function getUid( b ){
        return b.uid;
    }
class BodyImpulseResponseBehavior < Behavior

`Physics.behavior('body-impulse-response')`.

Responds to collisions by applying impulses.

Additional options include:
- check: channel to listen to for collisions (default: `collisions:detected`).
- mtvThreshold: apply partial extraction of bodies if the minimum transit vector is less than this value ( default: `1`)
  this will depend on your simulation characteristic length scale
- bodyExtractDropoff: every body overlap correction (underneith mtvThreshold) will only extract by this fraction (0..1). Helps with stablizing contacts. (default: `0.5`)
- forceWakeupAboveOverlapThreshold: force bodies to wake up if the overlap is above mtvThreshold ( default: `true` )