A good physical interaction is one that is responsive; it is like talking to a vegetable so nothing will get accomplish. When I was in the Atlanta Tech, they had an device that read your hand movements to control the screen. My group spent a solid 30 minutes trying to figure out a reliable way to control the screen. The interface was hard to control because it could not read fast or big motions, especially for up and down. One of us found a slightly more reliable method of turning the page but going up and down was nearly impossible. The device made interacting with the screen more difficult to control that it would have been better to use a mouse. I agree that it is hard to achieve due to the above example and the Xbox Kinect. The movements from the user gets lost in translation leading to an incoherent string of motions.