code: function(force, pos){
              pos = pos||{x:0,y:0};
              this.body.applyForce(cp.v(force.x, force.y), cp.v(pos.x, pos.y));
          }
docs: 施加力
  @memberOf PhysicsViewMixin
  @param  {Object} force 力，格式：{x:0, y:0}
  @param  {Object} pos 施力位置离重心相对偏移量，默认0，格式：{x:0, y:0}