I would define physical interaction as a cyclical process of input and output from a person or device or tool to another person or device or tool.
Good physical interaction should involve simple, intuitive and easy to understand design, with the ability for input and output/feedback from both parties (the person and the tool, etc.)
Things that are interactive:
- Raspberry Pi
- Cell Phones
Things that are NOT interactive:
- (dumb) TVs
I do agree with Crawford. There are just so many variables when thinking about creating something with good interactivity. How should it look, what should it do, how will the user use it, what happens when the user uses it in a way that it is not meant to be used, etc.? With so much to think about, it almost makes every interactive device a work of art!