Movement Script In Unity C#

I have been trying to make a movement script for my player in a 2D game but without success. I do not know why it is not working.

The problem is that the player isn't moving. I have a RigidBody attached and gravity on. (Not sure if gravity makes such a difference but I just thought to mention it.)

using UnityEngine;
using System.Collections;

public class PlayerMovement : MonoBehaviour {
   public Rigidbody rb;
   public float speed = 10;
// Use this for initialization
void Start () {

}

// Update is called once per frame
void FixedUpdate () {
    float mx = Input.GetAxisRaw("Horizontal");
    float mz = Input.GetAxisRaw("Vertical");

    Vector3 movement = new Vector3(mx, 0.0f, mz);
    Debug.Log(movement);
    rb.AddForce(movement * speed * Time.deltaTime);

  }
}