var t:Number = 0;
var dt:Number = 0.1;
var a:Number = 120;
var b:Number = -1.5;

world_mc._xscale = 1;
world_mc._yscale = 1;

world_mc.onEnterFrame = function() {
world_mc._xscale += a*Math.exp(b*t)*t*dt;
world_mc._yscale += a*Math.exp(b*t)*t*dt;
t += dt;
}