just a little test :)

physic.php

<?php

$i = 0;
$result = array();
while ($i <= 10) {
  if($i != 0){
		$x = $result[$i-1];
		$result[$i] = ((5.2 - (10.8 * $x)) * 0.04) + $x;
	}else{
		$result[0] = 0;
	}
	$i++;
}

print_r($result);