摩擦（簡単な方法）

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

// forked from _wonder's 摩擦
// forked from _wonder's base
package {
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.events.Event;
    
    public class Friction extends Sprite {
    		
    		private var ball:Ball;
    		private var vx:Number = 0;
    		private var vy:Number = 0;
    		private var friction:Number = 0.9;
    		
    		public function Friction() {
            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 {
        		vx *= friction;
        		vy *= friction;
        		ball.x += vx;
        		ball.y += vy;
        }
    }
}

import flash.display.Sprite;

class Ball extends Sprite {
	public var radius:Number;
	public var color:uint;
	
	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();
	}
}