Objects stop, but then pass through eachother, Rigidbody2D

I'll give the code for both of my objects, but essentially what happens is one object will collide with the other, and then they'll pass through each other. I think the problem is that I'm coding their movement incorrectly, but it could be one of the rigidbody settings. I think it should be an easy fix, but I couldn't find the solution online anywhere... Here's the inspector settings on the "ball" object (a square): Here's the inspector settings on the "Obstacle" object (a big rectangle):

Here's my code for the ball and the obstacle:

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Ball

---

using UnityEngine; using System.Collections;

public class Falling : MonoBehaviour {

 Vector3 velocity = Vector3.zero;
 public Vector3 gravity;
 public Rigidbody2D rb;
 
 // Use this for initialization
 void Start () {
         rb = GetComponent<Rigidbody2D>();
 }

 // Update is called once per frame, PHYSICS here
 void FixedUpdate () {
         velocity += gravity * Time.deltaTime;
         rb.AddForce(transform.position += velocity * Time.deltaTime);

 }

}

---

Obstacle

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using UnityEngine; using System.Collections;

public class Upward : MonoBehaviour {

 Vector3 velocity = Vector3.zero;
 public Vector3 AntiGravity;
 public Rigidbody2D rb;

 // Use this for initialization
 void Start () {
     rb = GetComponent<Rigidbody2D>();
     float RandomFl = Random.Range(-0.755f, 0.755f);
     transform.position = new Vector3 (RandomFl, -3.4f, -1f);
 }
 
 // Update is called once per frame
 void Update () {
     if (transform.position.y <= 3.35) {
         velocity -= AntiGravity * Time.deltaTime;
         rb.AddForce(transform.position -= velocity * Time.deltaTime);
     }
 }

}

If you guys could help me, that would be awesome! I can't find the solution online.

 Vector3 gravity = new Vector3(0,-20,0);
 
 void FixedUpdate()
 {   
     rb.AddForce(gravity, Force$$anonymous$$ode.Acceleration);
 }