function Force(fx, fy, life, easing) {
      var _this;
      _this = _Behaviour.call(this, life, easing) || this;
      _this.force = _this.normalizeForce(new Vector2D(fx, fy));
      _this.name = "Force";
      return _this;
    }
@memberof! Proton#
@augments Proton.Behaviour
@constructor
@alias Proton.Force

@param {Number} fx
@param {Number} fy
@param {Number} [life=Infinity] 			this behaviour's life
@param {String} [easing=ease.easeLinear] 	this behaviour's easing

@property {String} name The Behaviour name