AddForce(transform.up) works but AddForce(transform.forward) does not

Questions & Answers
1

// this works

if (Input.GetKeyDown(KeyCode.UpArrow))
        {

            Rigidbody2D tester = this.GetComponent<Rigidbody2D>();
            tester.AddForce(transform.up * 1000f);
        }

// i change it to this it does not work

if (Input.GetKeyDown(KeyCode.UpArrow))
        {

            Rigidbody2D tester = this.GetComponent<Rigidbody2D>();
            tester.AddForce(transform.forward* 1000f);
        }

Heres a screenshot:
https://snipboard.io/T0MXFK.jpg

2

Well, you work in a 2d setup here. So using transform.forward makes not much sense here. You only have the x and y axis in 2d which is transform.right and transform.up.