How can I turn my cube object to the direction it is traveling?

I have tried many different options with Quaternions and what not, but all I want is for my cube to face the way it is sliding. It can't be this hard...

This is the move function I have in place:

private void FixedUpdate () { // Adjust the rigidbodies position and orientation in FixedUpdate. Move ();

 }


 private void Move()
 {
     // Move the character with vectors
     Vector3 movement = transform.forward * cube_VerticalMovement * cube_Speed *Time.deltaTime;
     Vector3 movement2 = transform.right * cube_HorizontalMovement * cube_Speed *Time.deltaTime;
     Vector3 MoveVector = movement + movement2;

     cube_Rigidbody.MovePosition (cube_Rigidbody.position + MoveVector);

     // Turn the character in the direction of movement

 }