Bounce

HTML

<div class="ball"></div>

CSS

.ball{
    position:absolute;
    font-size:45px;
    background:#333;
    width:40px;
    height:80px;
    line-height: 78px;
    border-radius: 50%;
    margin:auto;
    left:50%;
    top:100px;
}

JavaScript

$(function () {
    toggle=1;
	function bounce(){	
            if(toggle == 1){
                $(".ball").animate({top:'-=80px'}, 1000); 
                toggle = 0;
            }else{
                $(".ball").animate({top:'+=80px'},1000); 
                toggle = 1;
            }
        }
		setInterval(bounce, 100);
});