Rigidbody2D AddForce: Why different phone speed and effect is not the same?

Unity Engine
1

This is my test code:

public void OnButtonClick()
    {
        m_objBall.GetComponent<Rigidbody2D> ().AddForce (transform.right * 1000);
        return;
    }

Click the button to shoot ball, why different phone speed and effect are not the same?
Must AddForce be called in FixedUpdate?

Android 6.0 ball speed is slower!
Android 5.0 ball speed is faster!
why???

2

Does anyone have a good idea? Thanks

3

I apply the force only once, what does frame rate has to do anything with this?

4

If AddForce be called in FixedUpdate, still have this problem Incredible, is this bug?