How to make an object with diffrent audio sources.

Im creating a game with a ball. When the ball touches the ground it makes one sound. Now what I want to do is to make that ball make a sound when its on ground and its velocity is greater then 0. What should I do.

My script:
var forse : float;
var maxSpeed : float;
var jumpforse :float;
var CanJump = true;
var fallforse : float;

function Update () {
if(Input.GetKey(KeyCode.W)) {
rigidbody.AddForce (Vector3.forward * forse);

}
	if(Input.GetKey (KeyCode.S)) {
	rigidbody.AddForce (Vector3.back * forse);
	
}
if(Input.GetKey (KeyCode.A)) {
	rigidbody.AddForce (Vector3.left * forse);
	
}
if(Input.GetKey (KeyCode.D)) {
	rigidbody.AddForce (Vector3.right * forse);
	
}		

if(rigidbody.velocity.magnitude > maxSpeed){
	rigidbody.velocity = rigidbody.velocity.normalized * maxSpeed;
}
if(Input.GetButtonDown ("Jump")) 
{
	if(CanJump == true) {
		rigidbody.AddForce (Vector3.up * jumpforse);
		
	}	
}	

}
function OnCollisionExit(collision : Collision){

if (collision.gameObject.name == "Terrain"){
	yield WaitForSeconds (0.25);
	CanJump = false;
	
}

}

function OnCollisionEnter(collision : Collision){

if (collision.gameObject.name == "Terrain"){
	CanJump = true;
	audio.Play();
	
	

}

}
function OnCollisionStay(collision : Collision){

if (collision.gameObject.name == "Terrain"){

	CanJump = true;
	
}	

}

var sound1 : AudioClip;
var sound2 : AudioClip;
var Change : boolean = false;
function OnCollisionEnter(Collision : col) {
if(col.gameObject.name== “Ground”) {
if(Change == true) {
Change == false;
AudioSource.PlayClipAtPoint(sound1, transform.position);
}
else {
Change == true;
AudioSource.PlayClipAtPoint(sound2, transform.position)
}
}
}

//You can now modify this script i just want to show you how to change the sounds.
//now when ball touch the floor every time sound will be changed.