Sliding/Moving Objects?

Heyy guys

I'm in need a little help, So I'm trying to make a game like 'Impossible Game' That was made on Ps3(That's all I know it from). But abit more advanced ( like more levels, different things etc.)

But I can't get the Cube to slide across the screen, It's only rotating.

He it is.

 var speed = 100;
 var jumpHeight = 8;
 
 private var isFalling = false;
 
 function Update () 
 {
     var rotation : float = Input.GetAxis("Horizontal") * speed;
     rotation *= Time.deltaTime;
     rigidbody.AddForce(Vector2.right * rotation);
     
     if(Input.GetKeyDown(KeyCode.Space) && isFalling == false)
     {
         rigidbody.velocity.y = jumpHeight;
     }
     isFalling = true;
 }
 
 function OnCollisionStay()
 {
     isFalling = false;
 }