AddExplosionForce won't have any effect.

Hey, I'm making a Sidescroller-Shooter-Game.

So I have my Character equipped with an RPG, that is shooting missiles. If the Missile hits a collider, it will instantiate an Explosion and Destroy itself. The Explosion got a Script attached, that will call AddExplosionForce on void Start.

I actually took the Script from the Scripting reference:

 using UnityEngine;
 using System.Collections;
 
 public class ApplyExplForce : MonoBehaviour {
     public float radius = 5.0F;
     public float power = 10.0F;
     public void Start() {
         Vector3 explosionPos = transform.position;
         Collider[] colliders = Physics.OverlapSphere(explosionPos, radius);
         foreach (Collider hit in colliders) {
             if (!hit)
             
             if (hit.rigidbody){
                 hit.rigidbody.AddExplosionForce(1000, explosionPos, 10, 3.0F);
             }
         }
     }
 }

In the next step I created a Cube and added a rigidbody to it. Nothing more. But if i shoot the Missile and it definitely creates the explosion, it doesn't have any effect on the Cubes. I tried to raise power and radius, but it didn't affect the cube.

I don't have an Idea what else I could try...

Hope someone could help me.