public class PlayerMovement : MonoBehaviour {
    public float speed;

    void FixedUpdate()
    {
        float moveHorizontal = Input.GetAxis ("Horizontal");
        float moveVertical = Input.GetAxis ("Vertical");

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

        rigidbody.AddForce (movement * speed * Time.deltaTime);
    }
    void OnTriggerEnter(Collider other)
    {
        if (other.gameObject.tag.Contains ("Wall") == true)
            Application.LoadLevel (0);
    }
}