how to cancel drag rigidbody in unity code example

Example: how to drag a 2d rigidbody in unity

// add this to your player. Make sure there is a rigidbody2d attached to it. private Vector2 direction; public float force = 1000; private Rigidbody2D r;  void Start () {     r = transform.GetComponent <Rigidbody2D> (); }    void Update {     if (Input.touchCount > 0) {         target = Camera.main.ScreenToWorldPoint(Input.GetTouch(0).position);         direction = (target.transform.position - transform.position).normalized;         r.AddForce (direction * Time.deltaTime * force);     } }