Closed system

The term closed system has different meanings in different contexts.

In physics

Further information: The concept of closed systems in physics

In classical mechanics

In nonrelativistic classical mechanics, a closed system is a physical system which doesn't exchange any matter with its surroundings, and isn't subject to any force whose source is external to the system. A closed system in classical mechanics would be considered an isolated system in thermodynamics.

In thermodynamics

Main article: Thermodynamic system

In thermodynamics, a closed system can exchange energy (as heat or work) but not matter, with its surroundings. An isolated system cannot exchange any of heat, work, or matter with the surroundings, while an open system can exchange all of heat, work and matter. For a simple system, with only one type of particle (atom or molecule), a closed system amounts to a constant number of particles. However, for systems which are undergoing a chemical reaction, there may be all sorts of molecules being generated and destroyed by the reaction process. In this case, the fact that the system is closed is expressed by stating that the total number of each elemental atom is conserved, no matter what kind of molecule it may be a part of. Mathematically:

$\sum_{j=1}^m a_{ij}N_j=b_i$

where $N_j$ is the number of j-type molecules, $a_{ij}$ is the number of atoms of element i in molecule j and b_i is the total number of atoms of element i in the system, which remains constant, since the system is closed. There will be one such equation for each different element in the system.

In quantum physics

Further information: Quantum field theory

In computing

Main article: Closed source software

In computing a closed system refers to software which the specifications and detail of implementation (typically source code) are kept secret, as opposed to open source systems.

In engineering

In an engineering context, a closed system is a bound system, i.e. defined, in which every input is known and every resultant is known (or can be known) within a specific time.

See also

• Glossary of systems theory
• Closed-circuit television (CCTV)
• Dynamical system
• Isolated system
• Open system (system theory)
• Thermodynamic system
• Closed cycle rocket engine