i have instantiate the prefab plz look at code..... but my problem is i want sphere

to fall on the plane…(i also added rigidbody to sphere and has enabled use gravity…but still sphere only rotates and do not fall on plane)…
plz look at my code

var theprefab:GameObject;
var siddhesh:boolean = false;

function Update () {
if (siddhesh==false)
{
Instantiate (theprefab,transform.position,transform.rotation);
siddhesh=true;
}
}

If you wants sphere fall on the plane no need to add any script with sphere. Just Simply Add the Rigid-body with sphere Try It.

now my prefab(sphere )is falling down on plane …now as soon as it falls on plane i want it to move in staright direction so i have used transform.translate…but still its not working…wht should i use in order to move sphere (my prefab)…here is code…

var theprefab:GameObject;
var siddhesh:boolean = false;
var speed :float= 5.0;
function Update () {
if (siddhesh==false)
{
Instantiate (theprefab,transform.position,transform.rotation);
siddhesh=true;
}

transform.Translate(Vector3(0,0,-speed) * Time.deltaTime);

}