In the first two chapters of “The Art of Interactive Design”, Chris Crawford defines “interaction” as “a cyclic process in which two actors alternately listen, think, and speak”. Based on this idea, I would say physical interaction is two objects making reactions to each other based on the information exchanging between them. All the storage equipments, SD card or USB drive, are not interactive because they do only information exchange but no reaction.
In the article from Bret Victor, he describes the popular screen technology as “Pictures Under Glass”,which deprives most parts of our useful natural sense. I totally agree with it. The Good physical interaction should be efficient, function well, emotional, and attractive. If the interaction could keep, even enhance human’s natural senses and abilities, it will reach these goals way more easier. Because the volume of informations human sense conveyed is so huge that makes more possibilities about reaction.