求前端的大大帮忙看看我的文字滚动为什么会卡顿

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<HTML xmlns="http://www.w3.org/1999/xhtml">
<HEAD>
<TITLE></TITLE>
</HEAD>
<BODY>
<DIV id="scrollobj" style="overflow:hidden;height:60px;width:250px;float:left;margin-top:120px;text-align:center;margin-left:80px">
        <span style="color:orange">13109999999 1989-06-01 1000元</span>
        <span style="color:orange">13109999991 1989-06-01 1000元</span>
        <span style="color:orange">13109999992 1989-06-01 1000元</span>
    </DIV>
    <script language="javascript" type="text/javascript">

    function scroll(obj) {
        var tmp = (obj.scrollTop)++;
        //
        if (obj.scrollTop == tmp) obj.innerHTML += obj.innerHTML;
        //当滚动条滚动了初始内容的高度时滚动条回到最顶
        if (obj.scrollTop >= obj.firstChild.offsetHeight) obj.scrollTop =0;
    }
    setInterval("scroll(document.getElementById('scrollobj'))",50);

    </script>
</BODY>
</HTML> 

...为什么我跑这个就不卡

html 看不懂啊……

我用多个浏览器试过,也不卡啊