jQuery: Find word and change every few seconds

Question

How can I change a word every 2-3 seconds using jQuery?

For example:

I have this:

    This is so
    <         


        
      

Answer 1

     $(document).ready(function(){ 
                setInterval(function(){
                      var current = jQuery(".animate-span .active");
                      var cIndex = jQuery(".animate-span span").index(current), cLength = jQuery(".animate-span span").length, nextSpan = null;
                      if(cIndex<(cLength-1)){
                       nextSpan =   jQuery(".animate-span span").eq(cIndex+1)        
                       }else{
                     nextSpan = jQuery(".animate-span span").eq(0);
                }
                     nextSpan.animate({top:0,opacity:1},500).addClass("active");

                      current.animate({top:45,opacity:0},500,function(){
                        jQuery(this).css({top:-40});
                    }).removeClass("active");
                },2000)
            });   

live demo here