rigidbody.Addforce doesn't move my bullet.

I'm working on a FPS, and I want to use rigidbody to launch my bullet. Here is my script so far

 using UnityEngine;
 using System.Collections;
 
 public class PlayerGunController : MonoBehaviour 
 {
     public GameObject bullet;
 
     void Update () 
     {
         if(Input.GetMouseButtonDown(0))
         {
             print("Pulled trigger");
             bullet.rigidbody.AddForce(Vector3.forward * 10);
         }
     }
 }

I did a little reading about Rigidbody in the script reference, then gave it a go. Doesn't work. The bullet gameobject is a sphere with a rigidbody attached to it. useGravity is off and isKinematic is on, no other settings were changed.

I click the button and see the message printed, but the sphere doesn't move. Any help?