Thermodynamics, Similarities between System and Control Volume
(a) System and Control Volume are defined by careful in description of their boundaries.
(b) System and Control Volume concepts are useful in permitting the interactions at the boundaries to be related to the changes occurring within them.
System and Control Volume Differences
(a) A system denotes a prescribed collection of matter while a control volume denotes a particular region of space.
(b) The system boundary may, and usually does, change shape, position and orientation relative to the observer. The control volume boundary does not,