After doing the two readings, I would venture a definition of “physical interaction” as the dynamic interplay of two or more entities that can transform one or both entities as a result of that interaction.
For instance: two different bacteria interact and both mutate as a result.
I found the Crawford’s discussion of how “interaction” is juxtaposed to just “reaction” and “communication” to be very thought-provoking.
Rather than see it as an either-or, I would place reaction-communication-interaction as points on a spectrum, with reaction located on the simple end (object A act, object B responds), communication as a more complicated encounter by two sides (both sides signal and indicate some degree of understanding) to a most complicated and meaningful encounter — interaction, whereby two sides communicate, react, but are somehow changed by the experience.
Viewing this discussion through a Jungian lens, signs would be more on the communicative side and symbols would be more of the interactive side.
A sign that says “the temple is on 5th street” serves a straight-forward function of information delivery, but a picture of mandala is more interactive because of the meaning invested in it. The mandala can transform the consciousness of the beholder, and the beholder can transform the meaning of the mandala, of which its pictorial representation is only a part. The sign is just a sign. (For more on signs and symbols, see here).
Similarly, a static painted circle could be more transformative than the most “interactive” app on the phone, which is bounded in the mental space of the person playing it. If the app is an interactive game, for instance, it’s interaction only goes so deep and the person remains fundamentally unchanged. However if the same person sees the static painted circle at the right time, and right place, they could be transformed.