Why can't I cd into a directory?

I am running Ubuntu 10.04.2 LTS. Why I can't I cd into the /var/www directory?

david@ubuntu:/var$ pwd
/var

david@ubuntu:/var$ ls -l
drwxrwxr-- 13 root root  4096 2011-02-26 21:53 www

david@ubuntu:/var$ cd www
-bash: cd: www: Permission denied

david@ubuntu:/var$ sudo cd www
sudo: cd: command not found

You need execute permission to cd into a directory.

sudo chmod o+x /var/www

There is some reason for prohibiting the ''others'' from entering the directory, no? So I would suggest to get root access to enter that directory, do some stuff, and leave it, dropping the sudo shell.

sudo -i 
cd /var/www
# do your thing
cd -
exit

Just a little further info, it would be wise to create a web user and group for your system and not have services running as root. Then you can also add users to that group if needed and not be giving root privileges out.