 Welcome back. Before continuing our discussion on open systems, an interesting nomenclature must be mentioned. In literature, open systems are often labeled as control volumes. This fact stems from history. Historically, closed systems were called as control mass systems and by default, open systems have been called as control volume systems. For closed systems, such a nomenclature is reasonably apt in the sense that the mass in the system does not change. It is a fixed mass. It does not leave the boundaries of the closed system. But for open systems, the boundaries are not necessarily constant. That is, it is not really a constant volume system or a control volume system. For turbines or nozzles, such a nomenclature is okay and the boundaries do not change there. But for example, if you consider an open system such as a tire which you are filling up with air, then the boundaries actually are shifting and it is still an open system because mass is crossing the boundaries and entering the system. So, this nomenclature is not really apt for open systems. However, because it is used widely, we will continue to use control volume as a substitute for open system even in this course and often when we write a subscript for open systems, we will put a CV for representing control volume. Thank you.