private function rotateX(ball:animation_ch15_Ball3D, angleX:Number):void
    {
     var cosX:Number = Math.cos(angleX);
     var sinX:Number = Math.sin(angleX);
     
     var y1:Number = ball.ypos * cosX - ball.zpos * sinX;
     var z1:Number = ball.zpos * cosX + ball.ypos * sinX;
     
     ball.ypos = y1;
     ball.zpos = z1;
    }