Why jquery class selector select items that has part of the classname?

<div class="carBig"></div>

<div class="car"></div>

<html>
<head>
</head>
<script type="text/javascript" src="jquery-1.2.6.pack.js"></script>
<script type="text/javascript">
    $(document).ready(function() {
    	$(".car").hide();
    });
</script>
<body>
    <div id=container>
    	<div class="carBig">Car Big</div>
    	<div class="car">Car</div>
    </div>
</body>
</html>

<html><head><title>Testing</title>
<script type="text/javascript" src="/js/jquery/jquery-1.2.6.min.js">
</script>
<script type="text/javascript">
$(document).ready(function() {
    $(".car").each(function() {
        $("#carResults").append($(".car").size());
        $("#carResults").append($(this).text());
    });
});
</script>
</head><body>
<div class="carBig">Big Car</div>
<div class="car">Regular Car</div>
<div id="carResults"></div>
</body></html>

Big Car
Regular Car
1Regular Car