[摩擦力の実装]動いている物体に摩擦を加える

/**
 * Copyright Nowloading_ ( http://wonderfl.net/user/Nowloading_ )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/sBG2
 */

package {
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.events.Event;
    public class friction1 extends Sprite{
        private var ball:Ball;
        private var vx:Number=0;
        private var vy:Number=0;
        private var friction:Number=0.1;
        public function friction1(){
            init();
        }
        private function init():void{
            stage.scaleMode = StageScaleMode.NO_SCALE;
            stage.align = StageAlign.TOP_LEFT;
            
            ball=new Ball();
            ball.x = stage.stageWidth/2;
            ball.y = stage.stageHeight/2;
            vx = Math.random()*10-5;
            vy = Math.random()*10-5;
            addChild(ball);
            addEventListener(Event.ENTER_FRAME,onEnterFrame);            
        }
        private function onEnterFrame(e:Event):void{
            var speed:Number = Math.sqrt(vx*vx+vy*vy);
            var angle:Number = Math.atan2(vy,vx);
            if(speed>friction){
                speed -=friction;
            }else {
                speed = 0;
            }
            vx = Math.cos(angle)*speed;
            vy=Math.sin(angle)*speed;
            ball.x+=vx;
            ball.y +=vy;
        }
    }
}
    import flash.display.Sprite;
     class Ball extends Sprite{
        public var radius:Number;
        public var color:uint;
        public var vx:Number =0;
        public var vy:Number =0;
        
        public function Ball(radius:Number = 40,color:uint = 0xff0000){
            this.radius = radius;
            this.color = color;
            init();
        }
        public function init():void{
            graphics.beginFill(color);
            graphics.drawCircle(0,0,radius);
            graphics.endFill();
        }
    }