Frozen Warnings

How does Apache determine which of your existing vhosts is the default?

Meaning:

• I have two vhost.conf files in /etc/apache2/vhosts/ - fu.vhosts.conf and bar.vhosts.conf. 
  
• Both of these were copied from vhosts.template
  
• I performed a find and replace on "dummy-host.example.com" to "fu", and "bar", respectively. 
  
• I copied web content into /srv/www/vhosts/fu and /srv/www/vhosts/bar
  
• No content exists under /srv/www/htdocs

When I type in the IP of the server, the "fu" site appears.  How do I set a another site to appear as the default?

Thanks!