Basic ideas that providing explanation to the movement of information in information systems were proposed in the light of regarding information as a kind of matter. It was suggested that information had both "momentum" and "energy". The momentum of information provided explanation for the dynamic behaviors, and the energy of information provided explanation for the static attributes. A Theory of Information Physics was also proposed to provide more integrated explanation to general information movements. Some common information-movement examples were discussed to provide support for the proposing theory.