Incremental acceleration with Imput

Hey, I'm supernew in Unity... I'm trying to figure how to make a cube move like an ice cube on a tray using the iphone accelerometer. So the trick is that if I increase the angle of inclination the cube has to accelerate incrementally and decelerates if I tilted the device to the opposite side. So far I'm playing with this code from the reference without any luck:

var speed = 10.0;

function Update () { var dir : Vector3 = Vector3.zero;

 dir.x = -Input.acceleration.y;
 dir.z = Input.acceleration.x;
 
 if (dir.sqrMagnitude > 1)
     dir.Normalize();
 
 dir *= Time.deltaTime;

 transform.Translate (dir * speed);

}

Can someone help me figure it out?

Thanks!