js 漩涡

What's the ball's orbit if they head for it's next ball.
<html>
<canvas id="ca"></canvas><script>
    ca.width=ca.height=1000;
    var centerX=ca.width/ 2,centerY=ca.height/2;
    var g=ca.getContext('2d');
    var ro=Math.min(ca.width,ca.height)/2/Math.sqrt(3),the=0;
    var r=15;
    var v=10;
    var cnt=7;
    function circle(x,y,r){
        g.beginPath();
        g.arc(x,y,r,0,360);
        g.closePath();
        g.fill();
    }

    function dot(ro,the){
        var x=centerX+ro*Math.cos(the),y=centerY+ro*Math.sin(the);
        circle(x,y,r);
    }

    function go(){
        var ax=ro*Math.cos(the),ay=ro*Math.sin(the);
        var bx=ro*Math.cos(the+Math.PI*2/cnt),by=ro*Math.sin(the+Math.PI/cnt*2);
        var dx=bx-ax,dy=by-ay;
        var d=Math.sqrt(dx*dx+dy*dy);
        var mx=(ax*v+bx*(d-v))/d,my=(ay*v+by*(d-v))/d;
        ro=Math.sqrt(mx*mx+my*my),the=Math.atan2(my,mx);
        //r*=0.98;
        //v*=0.99;
    }
    var move=setInterval(function(){
        if(Math.abs(ro)<0.001){clearInterval(move);return;}
       // g.clearRect(0,0,ca.width,ca.height);
        go();
        for(var i=0;i<cnt;i++)
        dot(ro,the+i*2*Math.PI/cnt);
    },100);
</script>
</html>
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