I can't get my 3d Player to jump uppwards when pressing space...?

so, i was making a 3d obstacle game, and apart from dodging objects, i want to jump over them, but when i press space it just keepss going like nothing... this is what i've done, im really new, so i was expecting this to happen anyways haha.

public class PlayerMovement : MonoBehaviour {

 public Rigidbody rigidb;


 public float uppwardsForce = 200f;

 void Start()
 {
     if (Input.GetKey("space"))
     {
         rigidb.AddForce(0, uppwardsForce * Time.deltaTime, 0);
     }
 }

}

if someone knows about this please tell me.