# Physical system

Physical system . A physical system is an aggregate of material objects or entities between whose parts there is a causal link or interaction (although not necessarily deterministic or causal in the sense of the theory of relativity theory).

Summary

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• 1 Characteristics that define a physical system
• 2 Classification according to environment
• 3 Isolated Physical System
• 4 Sources

Characteristics that define a physical system

• Have a location in space-time.
• Having a defined physical state subject to temporal evolution.
• Being able to associate a physical quantity called energy.

For the vast majority of physical systems, the most basic object that defines a physical system is the Lagrangian, which is a scalar function whose functional form summarizes the basic interrelationships of the relevant quantities to define the physical state of the system.

Classification according to environment

Physical systems can be open, closed or isolated, depending on whether or not they make exchanges with their environment: An open system is a system that receives flows ( energy and matter) from its environment. Open systems, by virtue of receiving energy, can do the work of maintaining their own structures and even increasing their information content. The fact that living beings are stable systems capable of maintaining their structure despite changes in the environment requires that they be open systems. A closed system only exchanges energy with its environment, in a closed system the entropy value is maximum compatible with the amount of energy it has. An isolated system has no interchange with the environment.

Isolated Physical System

For example, according to the general theory of relativity, an isolated system must meet quite restrictive technical conditions, known as asymptotic flatness. In special relativity theory, classical or thermodynamic , in general, the conditions are less strict and simply require that the system the movement of the particles that make up the system be restricted to a compact region of space-time.

An isolated system is a part or region of the universe , which due to its peculiar conditions can be considered in isolation from the rest of the universe for study. That a given physical problem can be treated as an isolated system requires peculiar conditions dependent on theory.