运行效果截图如下：
点击此处查看在线演示效果。
完整实例代码点击此处本站下载。
具体代码如下：
<!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>自由落体</title> <script src="https://www.jb51.net/jquery-1.7.1.min.js" type="text/javascript"></script> <script type="text/javascript" > $(document).ready(function () { }); var all_Height = 500; var a = 9.8; // 加速度 var v = 0; var prev_Time = 0; var prev_Speed = 0; var prev_Height = 0; var speed = 0; // 获取当前的高度 var getHeight = function (obj) { return obj.offset().top; } // 获取当前的速度 var getSpeed = function (time, a) { return time * a; } // 向下走时获得当前物体所走的路径 var getCurrentHeight = function (time) { return 1 / 2 * a * time * time; } // 向上走时获得当前物体所走的路径 var getCurrentHeight2 = function (speed, time) { return speed * time - 1 / 2 * a * time * time; } // 向下跑 function down() { prev_Time = 0; var interval = setInterval(function () { if (getHeight($(".obj")) < all_Height) { prev_Time = prev_Time + 0.1; var height = getCurrentHeight(prev_Time) + prev_Height; $(".obj").css("top", height + "px"); $(".info").append("<div>" + height + "</div>"); } else { speed = getSpeed(a, prev_Time); prev_Speed = speed; clearInterval(interval); up(); } }, 5); } // 向上跑 function up() { prev_Time = 0; prev_Speed -= 4; // 动能损耗 var interval = setInterval(function () { if (speed > 0) { speed = prev_Speed - getSpeed(a, prev_Time); prev_Time = prev_Time + 0.1; var height = all_Height - getCurrentHeight2(prev_Speed, prev_Time); $(".obj").css("top", height + "px"); } else { clearInterval(interval); prev_Height = $(".obj").offset().top; if (prev_Height < all_Height) { down(); } } }, 5); } function play() { alert('play'); down(); document.getElementById("obj").onclick = null; } </script> <style type="text/css"> body{ margin:0 0 0 0 ; background:#FFFFFF;} .title { text-align:center; color:#666666; border-bottom:2px solid gray; font-size:30px; line-height:100px; font-weight:bolder;} .obj { background-image:url('a.jpg'); width:50px; height:50px; position:absolute; top:0; left:0; } </style> </head> <body> <div> <div >自由落体大模拟<span>(点击图片让它落下)</span></div> </div> <div ></div> </body> </html>