//관성력
MovieClip.prototype.inertiaMove = function(widthX,heightY,g,fric){
        if(this._x + this.speedX > widthX - this._width/2){
                this.speedX = -1*this.speedX;
                this._x = widthX - this._width/2;
        }else if(this._x + speedX <0 + this._width/2){
                this.speedX = -1*this.speedX;
                this._x = 0 + this._width/2;
        }else{
                this._x += this.speedX ;
        }
        if(this._y + this.speedY > heightY - this._height/2){
                this.speedY = -1*this.speedY;
                this._y = heightY - this._height/2;
        }else if(this._y + this.speedY <0 + this._height/2){
                this.speedY = -1*this.speedY;
                this._y = 0 + this._height/2;
        }else{
                this._y += this.speedY;
        }
       
        this.speedY = this.speedY + g;
        this.speedX = fric*this.speedX;
        this.speedY = fric*this.speedY;
};

//포물선운동
MovieClip.prototype.parabolaMove = function(){
        this.vy = this.vy + this.g;
        this._x = this._x + this.vx;
        this._y = this._y + this.vy;
};