<p>横向系数：<input id="hp" type="text" value="0.1" /> (0-1)</p>

<p>纵向系数：<input id="vp" type="text" value="0.6" /> (0-1)</p>

<p>速度：<input id="sp" type="text" value="30" />(20-1000)

<input type="button" value="demo" onclick="demo(document.getElementById('hp').value, document.getElementById('vp').value, document.getElementById('sp').value)" /></p>

<div style="margin-left:600px;">

    <div id="fall" style="width:30px; height:30px; background:#f90; position:relative; right:0px; bottom:40px"></div>

</div>

<script type="text/javascript">

var i = null;

function demo(hp,vp,sp) {

    var f=document.getElementById('fall');

        f.style.right='0px';

        f.style.bottom='40px';

        i&&clearInterval(i);

    var h=1,v=1,hp=(hp>0&&hp<1)?hp:0.2,vp=(vp>0&&vp<1)?vp:0.5,sp=(sp>20 || sp<1000)?sp:30;

        i=setInterval(function(){

            if(f){

                var r=parseInt(f.style.right)+h,b=parseInt(f.style.bottom)-v;

                f.style.right=r+'px';

                f.style.bottom=b+'px';

                if(r>1000)clearInterval(i);

                if(b>-210){

                    v+=2

                } else {

                    h=(v>0)?v*hp:0;

                    v*=(v>0)?-1*vp:0

                }

            }

        },sp);

    }

</script>