Finger Swipe on Object

I have a sphere that I'm trying to move by swiping my finger across the screen, but I'm unable to figure it out. Any thoughts? I can't get the sphere (called Ball) to move. I'm brand new to Unity, but here's what I have so far:

using UnityEngine; using System.Collections;

public class BallMover : MonoBehaviour{

 private Vector2 startPos;
 private Vector2 endPos;
 private Vector2 touchPos;
 private Rigidbody rb;
 private Touch touch;

 void Start(){
     rb = GetComponent<Rigidbody> ();
 }

 void FixedUpdate ()
 {
     float speed = Time.time;
     float moveHorizontal;
     float moveVertical;

     // Check if user touches screen
     if (touch.phase == TouchPhase.Began)
     {
         // get the x and y coordinates of screen touch
         startPos = touch.position;
         endPos = touch.position;
         // set movement to 0
         moveHorizontal = 0.0f;
         moveVertical = 0.0f;
     }
     // Check if user removes finger from screen
     if (touch.phase == TouchPhase.Ended)
     {
         // get last finger touch coordinates
         endPos = touch.position;
         // record time it took to finish finger swipe
         //speed = Time.time - speed;
         // set movement to end touch minus begin touch for both x and y axis
         moveHorizontal = endPos.x - startPos.x;
         moveVertical = endPos.y - startPos.y;
         // create movement variable
         Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);
         // add force to object
         rb.AddForce(movement * speed);
     }
 }

}