There are multiple ways of characterizing systems. Of those I have come to understand to date, several of the most useful are as follows. Isolated, Open and Closed Systems Systems may be characterized as either closed or open. A closed system is one that does not need to interact with its environment to maintain its existence. Examples are atoms and molecules.
Mechanical systems are closed systems.
Open systems are organic and must interact with their environment in order to maintain their existence. People are open systems in that they must interact with their environment in order to take in food, water, and obtain shelter. People provide waste products to the environment in return. The examples previously illustrated in terms of the furnace, filling the water glass, adjusting the shower tap are all open systems as there are elements outside the system which are considered to have an effect yet are not elaborated. An open system may interact with its environment in a growth or balancing fashion.