<?php
if (isset($_POST['submit'])) {
  $wordChunks = explode(" ", $_POST['somewords']);
  for($i = 0; $i < count($wordChunks); $i++){
    echo "Piece $i = $wordChunks[$i] <br />";
  }

  $wordChunksLimited = explode(" ", $_POST['somewords'], 4);
  for($i = 0; $i < count($wordChunksLimited); $i++){
    echo "Limited Piece $i = $wordChunksLimited[$i] <br />";
  }
}
else {
?>
<form action="#" method="post">
  <input type="textfield" name="somewords" />
  <input type="submit" name="submit" value="Submit" />
</form>
<?php } ?>