The most common classification separates open systems from closed systems, that is, those that have strong links with the outside world from those that are characterized by functioning regardless of the environment that surrounds them
The closed systems They are those that have an autonomous behavior, and do not have an interaction with other physical agents located outside of it. There is no causal relationship or correlation with anything that is outside, and therefore they can survive on the basis of their own operating mechanisms. For instance: an inflated balloon, a television, a nuclear reactor.
There are two types of closed systems, according to whether the absence of exchange with the outside it is total (which happens in the case of isolated systems) or if there is no exchange of matter, but there is an exchange of energy (which happens in closed systems).
Examples of closed systems
It is usually called a closed system to those systems that have a deterministic and programmed behavior, and that they have a very small exchange of energy and matter with the environment: so small that it in no way intervenes with the normal development of the system.
Next, the approach to some examples of systems that can function as closed systems:
- A wind-up watch, which for its operation requires that there is no modification by temperature or the external environment.
- An airplane, that although it expels certain gases to the outside, needs in some cases to be perfectly closed so that life and breathing are possible at so many meters high.
- A nuclear reactor.
- An inflated balloon.
- A car battery.
- A perfectly built thermos so that the temperature is kept unchanged in the least.
- The planet earth (exchanges energy but not matter)
- The universe, understood as a totality.
- A TV.
- A pressure cooker that does not allow gas to escape.
Characteristics of closed systems
A characteristic that is peculiar to closed systems is that, the very definition of the absence of interaction with the outside it imposes that all the equations that describe the movement inside a system of this type can only depend on variables and factors contained in the system.
The choice of origin of time it is arbitrary, and therefore the equations of temporal evolution are invariant with respect to temporal translations: this implies that energy is conserved, which also fits the definition of these systems.
If a system is closed, then any small internal energy changes in the system are due to the balance of heat transfer and work done.
However, it is correct to say that if the system increases its energy by one thermodynamic process, the rest of the universe loses the same amount of energy. The first law of thermodynamics, for closed systems, is written as ΔU = ΔQ – ΔW.
- Isolated systems
- Open, closed and semi-closed systems