We do not interact with systems without first performing some physical action on a physical device. This paper shows how formal notations and formal models can be developed to account for the relationship between the physical devices that we actually press, twist or pull and their effects on systems. We use state diagrams of each but find we have to extend these in order to account for features such as bounce-back, where buttons or other controls are sprung. Critical to all is the fact that we are physical creatures and so formal models have to take into account that physicality.