How to add force in up direction of a 2d object in Unity

[Edit to include actual solution]

When using a Rigidbody you are agreeing to no longer modify the transform directly, and let it be controlled only by the rigidbody. By rotating using the transform you are not properly allowing the body to have angulart momentum, and can run into a host of differnet issues.

Instead, rotate your object through Rigidbody.MoveRotation(), or better: Rigidbody.AddTorque()

it's likely you're not actually rotating the transform and are instead rotating the sprite or a child of the transform. You can verify this by using:

You can also try adding the force relative, this should give you the correct direction:

rb.AddRelativeForce(Vector3.Up);