Причина ошибки?

Fatal error: Uncaught Error: Using $this when not in object context in H:\OSPanel\domains\KingKino\index.php:13 Stack trace: #0 H:\OSPanel\domains\KingKino\index.php(18): ClassName::lol() #1 {main} thrown in H:\OSPanel\domains\KingKino\index.php on line 13

class AnotherClass
{
public $name = 'hoh';
public static function ff () {
echo $this->name;
}
}
class ClassName extends AnotherClass
{
public static function lol () {
    echo $this->name;
}
}
$us = new ClassName();
$us::lol();

https://ideone.com/8OR80j