Not understanding how rigidbody2D.AddForce works

I know t$$anonymous$$s has been asked before but I'm not able to find any answer that's not too technical or vague for me (I'm really new to coding). I'm creating an Asteroids-like space shooter using Unity's 2D features, but I don't know how to make rigidbody2D.AddForce work to make the s$$anonymous$$p move forward using the W key. A clear "try t$$anonymous$$s code" answer with an explanation would be tremendously appreciated. I had made the game in 3D and it works fine with t$$anonymous$$s code:

   #pragma strict
     
     var thrust: int;
     var rotationSpeed: float;
     var thrustEmitter: ParticleEmitter;
     
     function Update () {
     
         if (Input.GetKey (KeyCode.A))
         transform.Rotate(Vector3.left * Time.deltaTime * rotationSpeed);
         if (Input.GetKey (KeyCode.D))
         transform.Rotate(Vector3.right * Time.deltaTime * rotationSpeed);
         
         if (Input.GetKey (KeyCode.W)){
             thrustEmitter.emit=true;
             rigidbody.AddForce(transform.forward*Time.deltaTime*thrust);
                 }
              
         else{
             thrustEmitter.emit=false;
             }
     }

When remaking the game in 2D, the rotation and particle emitter are working properly, but the s$$anonymous$$p's not moving forward. Here's the code I have right now for 2D (Thrust is set to 1000):

 #pragma strict
 
 var thrust: int;
 var rotationSpeed: float;
 var thrustEmitter: ParticleEmitter;
 
 function Update () {
 
     if (Input.GetKey (KeyCode.A))
     transform.Rotate(Vector3.forward * Time.deltaTime * rotationSpeed);
     if (Input.GetKey (KeyCode.D))
     transform.Rotate(Vector3.back * Time.deltaTime * rotationSpeed);
     
     if (Input.GetKey (KeyCode.W)){
         thrustEmitter.emit=true;
         rigidbody2D.AddForce(Vector2.up * thrust);
     }         
     else{
         thrustEmitter.emit=false;
         }    
 }

Thanks!