code: function (vel) {
              var fx = this.friction.x * me.timer.tick,
                  nx = vel.x + fx,
                  x = vel.x - fx,
                  fy = this.friction.y * me.timer.tick,
                  ny = vel.y + fy,
                  y = vel.y - fy;
  
              vel.x = (
                  (nx < 0) ? nx :
                  ( x > 0) ? x  : 0
              );
              vel.y = (
                  (ny < 0) ? ny :
                  ( y > 0) ? y  : 0
              );
          }
docs: apply friction to a vector
  @ignore