Prototype question

[Adam14]

I was reading about prototype last night, and thought I'd give it my first try. Now, I have a question...there are 8 instances of a MC on the stage, named bar1-bar8...and I have them growing, in succession, in _xscale...can anyone tell me why the code below makes each bar grow quicker than the last:

code:

---

onLoad = function () {

	_root.i = 1;

	_root.speed = 10;

};

MovieClip.prototype.bargrow = function() {

	if (_root["bar"+i]._xscale<=200) {

		_root["bar"+i]._xscale += _root.speed;

	}

};

_root["bar"+i].onEnterFrame = function() {

	_root["bar"+i].bargrow();

	if (_root["bar"+i]._xscale>=100) {

		i++;

	}

};

---

if this is really simple, and I look stupid, can I say my girlfriend wrote it? <just don't tell her I said that>

thanks, and I've attached a sample of the file if you want to see it.
Adam