# Collisions (occasionally) sticky - cant work out why!

**URL:** <https://forum.kirupa.com/t/collisions-occasionally-sticky-cant-work-out-why/253759>\
**Category:** programming\
**Created:** [March 4, 2008, 9:08pm UTC](https://forum.kirupa.com/t/collisions-occasionally-sticky-cant-work-out-why/253759 "2008-03-04T21:08:20Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![steve\_b](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@steve\_b](https://forum.kirupa.com/u/steve_b)\
**Post date:** [March 4, 2008, 9:08pm UTC](https://forum.kirupa.com/t/collisions-occasionally-sticky-cant-work-out-why/253759/1 "2008-03-04T21:08:20Z")

</div>

Hey, coming to the end of a bit of a nightmare project. One last hurdle.

There are 30-odd balls bouncing around the stage. I have got collision detection code from [Kirupa.com](http://Kirupa.com) ([http://www.kirupa.com/developer/actionscript/multiple\_collision.htm](http://www.kirupa.com/forum/../developer/actionscript/multiple_collision.htm)) which calls some code that determines the direction of the bounce. About 80% of the time it works, but every so often the balls stick together, orbit around each other for a bit and then are flung away. Ive been staring at this and I cant fix it. Could anyone help please?

Code as follows:

Collision Detection:

```php
for (m=0; m<totalObjects; m++) {
        circleA = targets[m];

        for (n=m+1; n<totalObjects; n++) {
            circleB = targets[n];
            circleA = eval(circleA);
            circleB = eval(circleB);

            var xdiff:Number = circleB._x - circleA._x;
            var ydiff:Number = circleB._y - circleA._y;
            var dist:Number = Math.sqrt(xdiff * xdiff + ydiff * ydiff);
                
                if (dist <= (circleB._width)) {
                    _root.manage_bounce(circleA, circleB);
                }
        }

```

Manage Bounce:

```php
function manage_bounce(ball, ball2) {
    dx = ball._x-ball2._x;
    dy = ball._y-ball2._y;
    angle = Math.atan2(dy, dx);
    mag_1 = Math.sqrt(ball.x*ball.x+ball.y*ball.y);
    mag_2 = Math.sqrt(ball2.x*ball2.x+ball2.y*ball2.y);
    direction_1 = Math.atan2(ball.y, ball.x);
    direction_2 = Math.atan2(ball2.y, ball2.x);
    new_xspeed_1 = mag_1*Math.cos(direction_1-angle);
    new_yspeed_1 = mag_1*Math.sin(direction_1-angle);
    new_xspeed_2 = mag_2*Math.cos(direction_2-angle);
    new_yspeed_2 = mag_2*Math.sin(direction_2-angle);
    final_xspeed_1 = ((ball.mass-ball2.mass)*new_xspeed_1+(ball2.mass+ball2.mass)*new_xspeed_2)/(ball.mass+ball2.mass);
    final_xspeed_2 = ((ball.mass+ball.mass)*new_xspeed_1+(ball2.mass-ball.mass)*new_xspeed_2)/(ball.mass+ball2.mass);
    final_yspeed_1 = new_yspeed_1;
    final_yspeed_2 = new_yspeed_2;
    ball.x = Math.cos(angle)*final_xspeed_1+Math.cos(angle+Math.PI/2)*final_yspeed_1;
    ball.y = Math.sin(angle)*final_xspeed_1+Math.sin(angle+Math.PI/2)*final_yspeed_1;
    ball2.x = Math.cos(angle)*final_xspeed_2+Math.cos(angle+Math.PI/2)*final_yspeed_2;
    ball2.y = Math.sin(angle)*final_xspeed_2+Math.sin(angle+Math.PI/2)*final_yspeed_2;
}

```