// 부드러운 움직임
MovieClip.prototype.smoothMove = function(speed,targetX,targetY){
        this._x += speed*(targetX - this._x);
        this._y += speed*(targetY - this._y);
};

//회전운동
MovieClip.prototype.rotateTo = function(targetX,targetY){
        var diffX = targetX - this._x;
        var diffY = targetY - this._y;
        this._rotation = Math.atan2(diffY,diffX)*180/Math.PI;
};

//탄성력
MovieClip.prototype.elasticMove = function(a,b,tx,ty){
        var tempx = this._x;
        var tempy = this._y;
        this._x = a*(this._x - tx) + b*(this.prevx - tx) + tx;
        this._y = a*(this._y - ty) + b*(this.prevy - ty) + ty;
        this.prevx = tempx;
        this.prevy = tempy;
};