Hey,

you could have a look into Robert Penners easing equations they were written for Actionscript, but the math is the same and can be easily adopted to processing. Here is an example:

1. float changeValue = 300;
   float startValue = 1;
   int duration = 200;
   
   void setup() {
     size(400, 400);
     smooth();
     stroke(0);
   }
   
   
   void draw() {
     background(255);
   
     float r = easeOutQuad(frameCount%duration, startValue, changeValue, duration);
   
     ellipse(width/2, height/2, r, r);
   }
   
   float easeOutQuad(float t, float b, float c, float d) {
     t /= d;
     return -c * t*(t-2) + b;
   }
   

cool, very nice