accessing a class from within a class

[I87]

how do I access a class from within a class?

I'll give an example that wont work, but it's what I want to do

class db{

function connect(){
//connect to db
}

function query(){ //query }

...

}

$Db = new db();
$Db->connect();

class wut{

function whatever(){

$Db->query($sql);

}}

$woot = new wut();
$woot->wut(); 

I've not tried it, but could I use db::query($sql) in the second class?
but, wouldn't I have to connect to the database via db::connect again since it's static or w/e?

edit
would doing something like

//in class two

var $h;

$h->query($sql);

//instead of just $woot->wut();
$woot->h = $Db;
$woot->wut(); 

work?

my schools blocked my host, so I can't find out