[Mnilionic]

может так?

if (!_parent.bounce) {
	_parent.speedXscale = _parent.speedXscale*_parent.friction + (_parent.xscale -_parent._xscale)*_parent.ratio;
	_parent.speedYscale = _parent.speedYscale*_parent.friction + (_parent.yscale-_parent._yscale)*_parent.ratio;
	_parent._xscale +=  _parent.speedXscale;
	_parent._yscale += _parent.speedYscale;
}

или даже так:

with(_parent){
	if(!bounce){
		speedXscale = speedXscale * friction + (xscale -_xscale) * ratio;
		speedYscale = speedYscale * friction + (yscale - _yscale)* ratio;

		_xscale += speedXscale;
		_yscale += speedYscale;
	}
}