physics/box2dPhysics.js
function Physics(width, height, ballRadius) {
  this._height = height;
  this._width = width;
  this._ballRadius = ballRadius || 0.2;
  this._world = null;
  this._ballScored = function () {
  };
  this._paddleFixtures = {};
  this._init();
}
function Physics(width, height, ballRadius) {
  this._height = height;
  this._width = width;
  this._ballRadius = ballRadius || 0.2;
  this._world = null;
  this._ballScored = function () {
  };
  this._paddleFixtures = {};
  this._init();
}
function Physics ( width , height , ballRadius ) { this . _height = height ; this . _width = width ; this . _ballRadius = ballRadius || 0.2 ; this . _world = null ; this . _ballScored = function ( ) { } ; this . _paddleFixtures = { } ; this . _init ( ) ; }
Initialize physics environment
@param width field width
@param height field height
@param ballRadius ball game radius
@constructor
Initialize physics environment