How to make div follow scrolling smoothly with jQuery?

Question

In my container there are sections/boxes, but the last one of these boxes should follow scrolling when none of the other boxes are visible.

So, when user sc

Answer 1

I needed the div to stop when it reach a certain object, so i did it like this:

var el = $('#followdeal');
    var elpos_original = el.offset().top;
    $(window).scroll(function(){
        var elpos = el.offset().top;
        var windowpos = $(window).scrollTop();
        var finaldestination = windowpos;
        var stophere = ( $('#filtering').offset().top ) - 170;
        if(windowpos=stophere) {
            finaldestination = elpos_original;
            el.stop().animate({'top':10});
        } else {
            el.stop().animate({'top':finaldestination-elpos_original+10},500);
        }
    });