I think the moment was lost on her:
Emma: I keep swinging it in circles and when I stop it keeps going in circles.
John: Emma, I believe you’ve discovered Newton’s Third Law of Motion!
Emma: Can you cut this ribbon off of this for me?
Late Update: I think maybe she knew I was wrong. I think it should have been Newton’s First Law of Motion. Although if she knew I was wrong, she would have told me so.