Unity- Moving an Object to the left on a Scrolling Background - unity3d

Question

I am trying to create a simple Infinite Runner game on Unity and ran into a problem. The task is to make a ball spawn on the floor and immediately begin to roll to the left towards the Player. I have tried a number of ways to implement it, but it does not seem to work. Here is my most recent attempt:
public class ObstaclePool : MonoBehaviour {
public GameObject columnPrefab;
public GameObject ballPrefab;
public int obstaclePoolSize = 5;
public float spawnRate = 3f;
private GameObject[] obstacles;
private int currentObstacle = 0;
private Vector2 objectPoolPosition = new Vector2(-15, -25);
private float timeSinceLastSpawned;
private float spawnXPosition;
private bool hasCalled = false;
private int dice;
bool beforeBall = false;
// Use this for initialization
void Start () {
timeSinceLastSpawned = 0f;
SetupObstacles();
}
private void SetupObstacles()
{
obstacles = new GameObject[obstaclePoolSize];
for (int i = 0; i < obstaclePoolSize; i++)
{
dice = Random.Range(1, 3);
if (dice == 1)
{
obstacles[i] = (GameObject)Instantiate(columnPrefab, objectPoolPosition, Quaternion.identity);
}
else if (dice == 2)
{
obstacles[i] = (GameObject)Instantiate(ballPrefab, objectPoolPosition, Quaternion.identity);
}
}
}
// Update is called once per frame
void Update () {
timeSinceLastSpawned += Time.deltaTime;
if (GameControl.instance.gameOver == false && timeSinceLastSpawned >= spawnRate)
{
timeSinceLastSpawned = 0f;
if (hasCalled == false)
{
spawnXPosition = 10f;
hasCalled = true;
}
else
{
spawnXPosition = Random.Range(6f, 10f);
}
if (obstacles[currentObstacle].transform.tag == "Ball")
{
spawnXPosition = Random.Range(9f, 10f);
obstacles[currentObstacle].transform.position = new Vector2(spawnXPosition, -1.84f);
ballPrefab.GetComponent<Rigidbody2D>().AddForce(new Vector2(-100f, 0) * 5);
beforeBall = true;
}
else {
if (beforeBall == true)
{
spawnXPosition = Random.Range(9f, 10f);
beforeBall = false;
}
obstacles[currentObstacle].transform.position = new Vector2(spawnXPosition, -7.08f);
Debug.Log(spawnXPosition);
}
currentObstacle++;
if (currentObstacle >= obstaclePoolSize)
{
currentObstacle = 0;
SetupObstacles();
hasCalled = false;
}
}
}
}
For a quick explanation of my code: I have an array of size 5. It holds the obstacles that I have created. When deciding what to put inside the array, I generated a random number (1 or 2). If it's a 1, I put in a column. If it's a 2, I put in a ball. These obstacles are spawned off-screen. Then, I move them in the actual scene after using random number to determine the X position.
This part in particular is where I try to implement it:
if (obstacles[currentObstacle].transform.tag == "Ball")
{
spawnXPosition = Random.Range(9f, 10f);
obstacles[currentObstacle].transform.position = new Vector2(spawnXPosition, -1.84f);
ballPrefab.GetComponent<Rigidbody2D>().AddForce(new Vector2(-100f, 0) * 5);
beforeBall = true;
}
I may have some remnants of stuff that I have been testing out, so some of the code may seem redundant and messy.
I also tried using Translate and Velocity with no success. I also have a ScrollingObject code and a RepeatingBackground code. I placed the ScrollingObject code in the Ball prefab too. (Also, tried taking it out -> ball rolls to the right). These codes come from the Unity tutorial.
RepeatingBackground:
public class RepeatingBackground : MonoBehaviour {
private BoxCollider2D groundCollider;
private float groundHorizontalLength;
// Use this for initialization
private void Awake () {
groundCollider = GetComponent<BoxCollider2D>();
groundHorizontalLength = groundCollider.size.x;
}
// Update is called once per frame
private void Update () {
if (transform.position.x < -groundHorizontalLength)
{
RepositionBackground();
}
}
private void RepositionBackground()
{
Vector2 groundOffSet = new Vector2(groundHorizontalLength * 2f, 0);
transform.position = (Vector2)transform.position + groundOffSet;
}
}
ScrollingObjects:
public class ScrollingObject : MonoBehaviour {
private Rigidbody2D rb2d;
// Use this for initialization
void Start () {
rb2d = GetComponent<Rigidbody2D>();
rb2d.velocity = new Vector2(GameControl.instance.scrollSpeed, 0);
}
// Update is called once per frame
void Update () {
if (GameControl.instance.gameOver == true)
{
rb2d.velocity = Vector2.zero;
}
}
}

Answer 1

It looks like you simply named the wrong object in your first example.
if (obstacles[currentObstacle].transform.tag == "Ball")
{
spawnXPosition = Random.Range(9f, 10f);
obstacles[currentObstacle].transform.position = new Vector2(spawnXPosition, -1.84f);
ballPrefab.GetComponent<Rigidbody2D>().AddForce(new Vector2(-100f, 0) * 5);
beforeBall = true;
}
Notice how here you added the force to the prefab, not an instantiated version of the prefab.

Answer 2

I played around a bit more and got it to work. I just wrote another script that added force to the object. I still do not understand why my original way did not work though.