How to add Jump control from touch on screen? ANDROID

hi, so i have this really simple 2D android game with a ball that uses the accelerometer to move from side to side, and i was wondering how i would get the ball to jump with just a touch anywhere on the screen (in Java). Here is my code so far:

#pragma strict

var speed = .2;
private var circ : float;
private var previousPosition : Vector3;

@script RequireComponent(Rigidbody)
function Start()
	//Find the circumference of the circle so that the circle can be rotated the appropriate amount when rolling
	circ = 2 * Mathf.PI * collider.bounds.extents.x;	
	previousPosition = transform.position;

function Update () {
    var dir : Vector3 =;

    dir.x = -Input.acceleration.y*.2;

    transform.position.x += dir.x;
	rigidbody.AddForce(dir * speed * Time.deltaTime);

function LateUpdate()
	var movement : Vector3 = transform.position - previousPosition;
	movement = Vector3(movement.z,0,  -movement.x);
	transform.Rotate(movement / circ * 360, Space.World);
	previousPosition = transform.position;	

You could add force to the ball using world direction Vector3.up and then multiply by a variable ( * popForce ).