I have followed the script to move the frog with wasd and the directional arrows but the frog does not move

private Animator playerAnimator;
private float moveHorizontal;
private float moveVertical;
private Vector3 movement;
private float turningSpeed = 20f;
private Rigidbody playerRigidbody;

// Use this for initialization
void Start () {

    // Gather componets from the player gameobject
    playerAnimator = GetComponent<Animator> ();

    playerRigidbody = GetComponent<Rigidbody> ();

}

// Update is called once per frame
void Update () {

    // Gather input from the keyboard
    moveHorizontal = Input.GetAxisRaw ("horizontal");
    moveVertical = Input.GetAxisRaw ("Vertical");

    movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);

}

void FixedUpdate () {

    // If the players movement Vector does not equal 0 ...
    if (movement != Vector3.zero) {

        //...then create a target rotation based on the moment vector...
        Quaternion targetrotation = Quaternion.LookRotation(movement, Vector3.up);

        //...and create another rotation that moves from the current rotation to the target rotation
        Quaternion newRotation = Quaternion.Lerp(playerRigidbody.rotation, targetrotation, turningSpeed * Time.deltaTime);

        //...and change the players rotation to the new incremental rotation...
        playerRigidbody.MoveRotation(newRotation);

        //...then play jump animation
        playerAnimator.SetFloat("Speed", 3f);
    } else {
        //otherwise do not play the jump animation
        playerAnimator.SetFloat("Speed", 0f);
    }
}