So I've got classes Rect, MotileRect, and GravRect. Rect is an on-screen rectangle, MotileRect can move, and GravRect is *supposed* to pull MotileRects in toward it. Here they are:

1. class Rectangle {
     PVector pos;
   
     int h;
     int w;
   
     int r;
     int g;
     int b;
   
     Rectangle (PVector inpos, int inw, int inh, int inr, int ing, int inb) { //define with a vector
       pos = inpos;
       h = inh;
       w = inw;
       r = inr;
       g = ing;
       b = inb;
     }
   
     void render () {
       fill(r, g, b);
       noStroke();
       rect(pos.x, pos.y, w, h);
     }
     float getCX() { //get center-x
       return pos.x-(w/2);
     }
     float getCY() { //get center-y
       return pos.y-(h/2);
     }
   }
   
   class MotileRect extends Rectangle {
     PVector speed; //in pixels per 1/10th second.
     Trigger timer;
     MotileRect(PVector inpos, int inw, int inh, int inr, int ing, int inb, PVector inspd) {
       super(inpos, inw, inh, inr, ing, inb);
       speed = inspd;
       timer = new Trigger(10);
     }
     void update() {
       while (timer.fires ()) {
         pos.add(speed);
       }
     }
   }
   class GravRect extends Rectangle {
     float magnitude;
     GravRect (PVector inpos, int inw, int inh, int inr, int ing, int inb, float inmag) {
       super(inpos,inw,inh,inr,ing,inb);
       magnitude = inmag;
     }
     void affect(MotileRect target) {
       PVector effect = new PVector( magnitude/(pos.x-target.pos.x), magnitude/(pos.y-target.pos.y));
       target.speed.add(effect);
     }
   }
   

You can get the whole text of the program, to see what I'm trying to get at, here: http://pastebin.com/XddM4UL1

The problem is that my current implementation of gravity... doesn't work. It flings the rect it's supposed to be sucking in ALL OVER THE PLACE, in a way that's not consistent with anyone's laws of gravity, except maybe the LHC people. Anyway, what code should I use to make the gravity work?