I would define physical interaction as a constant passing of information between both parties interacting until one of them wishes to stop interacting. I think good physical interaction is constant and without any confusion, so that the person can gain the expected result almost without having to think about it every time. I would say that a lot of computing elements that we use regularly are not interactive, but instead programmable. For things like projectors, TVs, calculators, and many things of that nature it is more of a task processor, where you tell it instructions, like go to a certain channel, read from a certain wire, add two numbers. There is very little interaction other than perhaps the first passing of data one way. Something like a car is very interactive however, because the person is constantly telling the machine what to do and the machine is constantly reacting to exactly what the person is telling it at the time. I think interaction in my terms is fairly difficult to achieve because of the seamlessness of the interaction needed.