title: Collision detection not working unity
body: <p>First, I know that this question has been asked a lot, but I cant find a solution, so mi problem is, Im making an educational game, and I have a vein and the blood flow (with many box colliders) and a single blood cell (also with a box collider) however i want the cell to destroy when it reaches the wall collider, but it doesn't it just stays there, here is the project!</p>
  
  <p><a href="http://tinypic.com/r/10706es/9" rel="noreferrer">http://tinypic.com/r/10706es/9</a> </p>
  
  <p>(cant upload images because of my reputation, sorry)</p>
  
  <p>The collider where I want to destroy my cell is the pink collider, however when it touches it it just does nothing, here's my script</p>
  
  <pre><code>using System.Collections;
  using System.Collections.Generic;
  using UnityEngine;
  
  public class collision : MonoBehaviour {
      // Use this for initialization
      void Start () {
      }
  
      // Update is called once per frame
      void OnCollisionEnter(Collision col)
      {
          print("hihi");
          if (col.gameObject.tag == "Collider")
          {
              Destroy(gameObject);
          }
      }
  }
  </code></pre>
  
  <p>Also, here is the AddForce script</p>
  
  <pre><code>using System.Collections;
  using System.Collections.Generic;
  using UnityEngine;
  
  public class AddForce : MonoBehaviour {
  
      public float thrust;
      public Rigidbody rb;
      private Vector3 up;
      private bool move;
  
      void Start()
      {
          rb = GetComponent&lt;Rigidbody&gt;();
          up = new Vector3(0, 1, 0);
          move = false;
      }
  
      void FixedUpdate()
      {
          if (Input.GetKey("space"))
          {
              if (rb.velocity.magnitude &lt; 5)
                  rb.AddForce(up * thrust);
              move = true;
          }
  
          else
          {
              if (move == true)
                  rb.velocity = new Vector3(0, -0.5F, 0);
          }
  
  
      }
  }
  </code></pre>
  
  <p>thanks for your help guys! :D</p>