I would define physical interaction as being the process of two parties alternatively listen, think and act.
Good physical interaction requires constant action between the two parties as they both listen and think between each interaction.
I would say an elevator is interactive in the sense that the elevator will usually make a noise when it has arrived to the destination and so the person knows it has stopped without having to watch the door, of the elevator, to see if it has opened.
Interactivity is all about the action between two parties in my opinion, so I agree with what Chris Crawford says in his analysis of the difficulty of interactivity. I had to study Latin for three years and understand completely what he means about the importance of verbs in the language and that is probably the largest difference between Latin and English.
