[]一个按钮按下弹起怎么加缓动效果

private function pm_down():void
{
var scaleValue:Number = 0.9;
mainPage.pm_main.scale(scaleValue, scaleValue);

}
private function pm_up():void
{

var scaleValue:Number =1;
mainPage.pm_main.scale(scaleValue, scaleValue);
}