Free fall and transformation of object very slow on iPod Touch 4

I'm using the below script to do a papertoss kind of game. My directions and velocity are working well. But, when the object moves ( either free falls or under the influence of AddForce ), I can see a frame by frame motion of the object rather than a smooth flow.

Any idea what I'm doing wrong?

var projectile : GameObject; var clone;

var distance: Transform; var Prefabball : GameObject;

var elevationAngle : Vector3; var throwForce : int;

var angle ="10"; var force=10; var shouldApply=false; var touchStart: Vector3; var touchEnd : Vector3; var ball:GameObject; var v:Vector3;

function Update () { for (var i = 0; i < Input.touchCount; ++i) {

     if (Input.GetTouch(i).phase == TouchPhase.Began) {
      touchStart = Input.GetTouch(i).position;
     }
    
     else if (Input.GetTouch(i).phase == TouchPhase.Ended) {
      touchEnd=Input.GetTouch(i).position;

Launch(); } }

}

function FixedUpdate() {

}

function Launch() { var p1:Vector3 = new Vector3(); var p2 :Vector3 = new Vector3(); touchStart.z = Camera.main.nearClipPlane+.1f; //push it a little passed the clip plane for camera, just to make sure its visible on screen touchEnd.z = Camera.main.nearClipPlane+.1f; p1 = Camera.main.ScreenToWorldPoint(touchStart); p2 = Camera.main.ScreenToWorldPoint(touchEnd); ball=GameObject.Find("PaperBall");

     v = (p2-p1);
     v.z=-1*Vector3.Distance(p2,p1);
     ball.rigidbody.AddForce(v*1000,ForceMode.Impulse);

     shouldApply=true;

}