RigidBody2D.addForce not working when called via UIButton

I am applying custom "gravity" to my ball object via a constant force using FixedUpdate because I don't want to use the typical downward pull, but I want to also add an impulse force (to make the ball jump) when the player taps a button. I thought the easiest way to do this would be to just make the button on click function call an opposite force as the custom gravity - in the code below I'm trying to use 3 for gravitationalPull and -5 for jumpForce - but nothing is happening when I press the button. The button does call the function, I added a log message to test this. And the console gives no errors.

Code (CSharp):

1. public class Gravity : MonoBehaviour {
2.  
3.     public GameObject ball;
4.     public float gravitationalPull;
5.     public float jumpForce;
6.  
7.     void FixedUpdate () {
8.         ball.GetComponent<Rigidbody2D> ().AddForce ((this.transform.position - ball.transform.position).normalized * gravitationalPull);
9.     }
10.  
11.     public void jump() {
12.  
13.         ball.GetComponent<Rigidbody2D> ().AddForce ((this.transform.position - ball.transform.position).normalized * jumpForce, ForceMode2D.Impulse);
14.  
15.     }
16.  
17. }

 

Bad testing on my part. Due to forces also being applied via surface effectors I just needed to increase the force value... a lot. 800 works a lot better than 5.